2 CPUs in servers are better than 1 CPU IMHO.
1) Total cost of ownership is far better on a single server with multiple cpus, you do not have to draw as much from the wall
2) You do not have to keep up on warranties for 2 single cpu servers with more hardware to break (twice the hard disks to break, twice the psus to fry..)
I could go on for a while with these, but here are some things that you might want to think about.
What type of software do you use and how is it's licensing model, it it "per server" , "per core" , "per cpu" ? All of these things could end up costing you less or more.
Load balancing is a good thing, can't do it on one server though
If costs permit, 2 multi-processor systems would be the way to go!