I am interested in establishing a wireless link between two locations that are about 2000' apart. There is some obstruction (so not fully LOS) but mostly just a few trees etc.. with the antennas up a few feet. My goal is to achieve a significantly faster link between these two points than the 1mbps upstream available on their internet connections.

Both locations are using dd-wrt routers for their main internet connections, so we can arrange static routing rules as we see fit to make both networks see each other. My plan is to use a pair of ubiquiti XtremeRange9 900mhz cards paired with a decent yagi at each end, and I'm planning on plugging this card into a mikrotik router board; perhaps the RB411?

My question is if a setup like this will work (is the RB411 sufficient?) and what kind of throughput I can expect across this link roughly (3mbps? 10mbps? 50mbps?)

Throughput depends on: channel size, modulation, signal strength, signal quality, noise floor level, interference levels, etc.

At 900 MHz you should be okay without a completely clear LOS, especially at such a short distance. Just remember that 900 MHz can be plagued by interference.

The RB411 should be sufficient for what you require.