have you tried it fresh, no ipv6, no tunnel, no extra firewall ?

Current:
DOWNLOAD 12.09 Mbps
UPLOAD 36.14 Mbps
Virgin Media<->Vodafone IE

Previous:
DOWNLOAD 341.11 Mbps
UPLOAD 35.96 Mbps
Virgin Media<->IP Telecom

router-pdn-export.rsc

Some questions:
I will assume that your WAN connection is Fiber from Virgin Media -- so is the Cisco GigE SFP module white-listed [approved] by Virgin?
Do you know the SYNC rate that Virgin is using ... is it 1.25G or 2,5G?

From your description of the issue my assumption would point to the wrong transceiver sync rate which usually means you have to use a module that is approved by Virgin for it work properly. The Other issue is that The RB4011 does not support Passive DAC modules and SFP GPON modules --- so this usually means that if you want to use the RB4011 SFP+ port for WAN you cannot do that --- instead you will need to use one of your Ethernet Ports like ether1 ... and the connectivity chain for that method is via a Media Converter that connects to Virgin using an approved SFP module and from the Media Converter to ether1 on the RB4011.

I have no experience with Virgin Media -- so I am just giving you some possibilities. Perhaps some other user who does have experience using Virgin and the RB4011 can chime in with how they establish connectivity.

I ended having to swap the cisco device back in. Having tried every permutation of interfaces, MSS clamping, doing packet captures (shed loads of DUP ACKs)

I ended having to swap the cisco device back in. Having tried every permutation of interfaces, MSS clamping, doing packet captures (shed loads of DUP ACKs)

If you sincerely want to be helped you need to answer some of the questions asked -- which questions you have chosen to avoid.

General Configuration
Network access	Allowed
Maximum Number of CPEs	10
Baseline Privacy	Enabled
DOCSIS Mode	DOCSIS 3.0
Config file	CH7465LG_cm_res005_v4-sip.bin

Primary Downstream Service Flow
SFID	200126981
Max Traffic Rate	10485760 bps
Max Traffic Burst	16320 bytes
Min Traffic Rate	0 bps
SFID	200126980
Max Traffic Rate	160000 bps
Max Traffic Burst	3044 bytes
Min Traffic Rate	12000 bps
SFID	200126979
Max Traffic Rate	385200000 bps
Max Traffic Burst	42600 bytes
Min Traffic Rate	0 bps

Primary Upstream Service Flow
SFID	200118791
Max Traffic Rate	2097152 bps
Max Traffic Burst	16320 bytes
Min Traffic Rate	0 bps
Max Concatenated Burst	16320 bytes
Scheduling Type	Best Effort
SFID	200118790
Max Traffic Rate	160000 bps
Max Traffic Burst	3044 bytes
Min Traffic Rate	12000 bps
Max Concatenated Burst	1522 bytes
Scheduling Type	Best Effort
SFID	200118786
Max Traffic Rate	38520000 bps
Max Traffic Burst	42600 bytes
Min Traffic Rate	0 bps
Max Concatenated Burst	42600 bytes
Scheduling Type	Best Effort

Downstream bonded channels
Channel	Frequency (Hz)	Power (dBmV)	SNR (dB)	Modulation	Channel ID
1	482000000	0	38	256qam	10
2	187000000	0	37	256qam	2
3	195000000	0	38	256qam	3
4	203000000	0	38	256qam	4
5	474000000	0	37	256qam	9
6	179000000	0	37	256qam	1
7	490000000	0	38	256qam	11
8	498000000	1	38	256qam	12
9	506000000	1	38	256qam	13
10	514000000	1	38	256qam	14
11	522000000	2	38	256qam	15
12	530000000	1	38	256qam	16
13	634000000	2	37	256qam	20
14	642000000	2	37	256qam	21
15	650000000	2	38	256qam	22
16	658000000	1	38	256qam	23
17	666000000	2	38	256qam	24
18	674000000	2	37	256qam	25
19	682000000	2	38	256qam	26
20	690000000	2	38	256qam	27
21	698000000	2	38	256qam	28
22	706000000	2	37	256qam	29
23	714000000	4	38	256qam	30
24	722000000	4	38	256qam	31

Downstream bonded channels
Channel	Locked Status	RxMER (dB)	Pre RS Errors	Post RS Errors
1	Locked	38.605	1147773538	9
2	Locked	37.356	1145937620	11
3	Locked	38.605	1145938123	18
4	Locked	38.605	1145938501	14
5	Locked	37.636	1145938064	10
6	Locked	37.636	1145933045	36
7	Locked	38.605	1145934339	19
8	Locked	38.605	1145935447	8
9	Locked	38.605	1145938971	11
10	Locked	38.605	1145939827	3
11	Locked	38.983	1145940639	13
12	Locked	38.605	1145932941	14
13	Locked	37.636	1145941303	33
14	Locked	37.636	1145942449	62
15	Locked	38.258	1145943702	27
16	Locked	38.605	1145944374	55
17	Locked	38.983	1145945483	40
18	Locked	37.636	1145947871	75
19	Locked	38.605	1145948761	64
20	Locked	38.605	1145949602	65
21	Locked	38.605	1145952087	84
22	Locked	37.636	1145950848	60
23	Locked	38.605	1145954068	65
24	Locked	38.605	1145952893	54

Upstream bonded channels
Channel	Frequency (Hz)	Power (dBmV)	Symbol Rate (ksps)	Modulation	Channel ID
1	32800000	39	5.120	64qam	2
2	60200000	41	5.120	64qam	6
3	39400000	40	5.120	64qam	3
4	53600000	43	5.120	64qam	5
5	46000000	39	5.120	64qam	4

Upstream bonded channels
Channel	Channel Type	T1 Timeouts	T2 Timeouts	T3 Timeouts	T4 Timeouts
1	2.0	0	0	2	0
2	2.0	0	0	1	0
3	2.0	0	0	1	0
4	2.0	0	0	3	0
5	2.0	0	0	2	0

My apologies I misunderstood.

Is you Cable Gateway in Bridge mode?
The power levels are excellent and your RoS code looks good to me. Confirm that your Ethernet cable is good.very strange that you’re not getting the throughput ..... perhaps a defective port, try another port.

Also make sure to shutdown your Cable modem, wait for 5 minutes then repower ... that may force a new profile for a different device especially when bridge mode is used.

1. Copper SFP as WAN link
2. Ether1 as WAN link
3. bond of ports ether5 and ether10 as WAN link

Something is definitely wrong with your RB4011 ... try one more process of running netinstall-6.45.1 .... this will eliminate any form of corruption in the NAND memory and reinstall ROS -- then proceed with your Copper SFP as WAN link to see if that works -- it should and if it does not then I would suggest that you send MikroTik support your supout.rif file for their observations and suggestion -- if this is a new unit or under warranty you may be able to RMA it based on MikroTik Support's observations of the supout.rif.

Something is definitely wrong with your RB4011 ... try one more process of running netinstall-6.45.1 .... this will eliminate any form of corruption in the NAND memory and reinstall ROS -- then proceed with your Copper SFP as WAN link to see if that works -- it should and if it does not then I would suggest that you send MikroTik support your supout.rif file for their observations and suggestion -- if this is a new unit or under warranty you may be able to RMA it based on MikroTik Support's observations of the supout.rif.