Hi,
We have around 10 webservers behind the same IP. Currently, a virtual machine (dual vcpu 1.6ghz) with 2gb of RAM is the REVERSE PROXY to access the internal servers. Nevertheless, this machine is not dedicated to this function, perform it very well.
I found and article to handle multiple web servers with MIKROTIK: http://wiki.mikrotik.com/wiki/Multiple_Web_Servers
We have two RB750G. We tested with 1 webserver and works GREAT. The problem is, performance was degrated. The average load time with the APACHE REVERSE PROXY for the home page was 4 seconds while using MIKROTIK was 6 seconds (always testing with clean cache).
Of course, the apache box is much larger, but Mikrotik is dedicated and more lightweight platform.
I'm not sure if this results are OK or I miss configured something.
Regards
Hernán.