servers = numbers to crunch and a huge amount of ram is needed.
more cores = more numbers can be crunched in parallel.
so find a multi core that fits your budget, hyper-threading would help as well. the problem is how much ram would you require to support them, the number of people counts as well.
consumer boards only has more or less than 6slots of ram, server boards on the other hand, has tons, specifically more than a dozen BUT theres one problem, server boards requires a different kind of ram, way more expensive than desktop ram.
the AMD Phenom II x6 1055t 2.8ghz should work well for your need, just find a board with 6-8slots and fill them up with 4gbs of ram. an i7 with hyper-threading would make a good cruncher too, 6slots would be standard for rams and they are on triple channel as well(old LGA1366 socket).
server builds on the other hand, is good, but costs alot so you know what i mean~