i7 all the way.
ETA: Forget Newegg. They were good, but now they suck.
Go to www.acmemicro.com Get a Supermicro motherboard (or a Gigabyte if you're into overclocking,) the i7 CPU, and be happy.
I'm a VAR who builds video editing workstations. I've been using ACME for about 20 builds now, and they are GREAT. I've never had an issue with any of the systems they've built for me. Their pricing is excellent, and they are very customer oriented.
It's a great time to buy computers. You can get workstation performance for desktop prices. Set a budget, and max out your hard drive subsystem speed and your motherboard specs. Graphics cards are a dime a dozen, and RAM is cheap. Fill it up. Don't forget good clean power. Way too many people cheap out on power supplies, and they pay the price down the road.
If you can afford SAS drives, build yourself a little RAID-10 and be happy. Or, build a RAID-10 out of SATA drives, and be pretty darned happy.