Dual Dual core Opteron System, Is there any point buying it?

I currently have a Dual 1.6GHz Opteron system It is far too slow for what i need to do which is Video rendering.

Do I just purchase 2 single core 2.6Ghz CPUs for about £1000 or is it worth buying 2 dual core 2.2Ghz CPUs giving me 4 processors for £1650?

Is there any software that would be able to use all 4 processors? I use Adobe Premiere Pro, Canopus Pro Coder 2 and Dr Divx.

Any advice on the best way to boost performance would be greatly apprecialted.

Other system info
Motherboard Tyan Thunder K8W
RAM 4GB DDR 400 Twin X ECC
Graphics Radeon 9800pro AGP8x
HDD 3000GB SATA RAID

2 Single Core model Opterons running at 2.6GHz each would be more cost effective and faster / core.

If you have highly parallelized applications then the 4 cores would be faster overall however each core by itself would be slower so all clock sensitive applications wouldn't run quite as fast as they would on the 2.6GHz single cores.

A lot would depend on your OS' scheduling policy too and other factors.

Here are some disk benchmarks on FC3 i386 [LEFT] and FC3 x86_64 [RIGHT] on a Dual Opteron with RAID5:

https://spare2.com/bench/index.html

If you were to run Linux x86_64 you would definitely get better performance!

Linux can run some windows games and apps but I am not sure if your apps would run.

Linux SMP support is really awesome much better than competing operating systems.