I/O is huge, as we'll be streaming and processing lots of image data.
If this is true and the newer processor is more expensive, I'd tell the salesman to go find another chump. According to wikipedia, they're both based on the same Nehalem architechure. About the only differences are clock speed, your existing processor uses a faster 1333Mhz bus, and the E5630 draws less power. Spend the money on better disks instead, or at least more RAM.
On the other hand, the wikipedia also lists the E5630 as costing much less money. If this is true, and you really are I/O-bound, then the sales guy knows what he's doing. He's saving you money by selling you a cheaper processor because the more-expensive one was mostly wasted. Another option, if you are I/O bound, is the L5618. This shows the same price as the E5630 and is another 25% slower, but uses 1/2 the electricity. So that's an option if your business is interested in going green.
If I you do want a CPU upgrade, the one thing I might do is go for an E5650. This is a six-core processor, with up to 12 simultaneous threads without the need for context switching when you consider hyperthreading. Since your application calls for up to 12 threads, that could mean a serious bump. But only if you are CPU bound rather than I/O bound.