Under Vista
ATA-6 133Mbit/sec gets rated 4.6
SATA2 300Mbit/sec gets rated 5.9
The system I have at the moment was fairly cheap to put together
£250 in all
AMD Series-7 Motherboard (760FX) - £35
AMD Athlon X2 3800+ (2.0GHz) - £35
Kingston 667MHz 2x512MB ECC (1GB) - £26
ATi Radeon HD 2600 XT x16 PCI-e (256MB) - £60
Western Digital SATA-II HDD (320GB) - £40
Samsung DVD±RW SATA-II (48x24x16x) - £20
Cube Case w/300watt PSU - £45
That runs just about everything with maxed out graphics at atleast 60fps. Only game I think of that it struggles with is Crysis Maxed out, but tbh unless you're running it in DirectX10... Medium and High graphics don't actually look different enough to warrent the performance difference.
I was for a while using a slighly different motherboard (AMD nFORCE 403 with NVIDIA 6100 Shared 256MB)
Ratings Vista gave before:
Processor: 4.2
Memory: 3.8
Graphics: 3.0
Gaming Graphics: 3.2
Primary Hard Disk: 4.8
After the upgrade of motherboard and graphics card:
Processor: 4.8
Memory: 4.5
Graphics: 5.9
Gaming Graphics: 5.5
Primary Hard Disk: 5.7
I've yet to really tinker, but possibly more amazingly is that all of this is running on a 300watt PSU. With my old X1600 on my other system anything other than a 450watt PSU would cause it to reboot with power spikes. Particularly when playing games. So it's a damn sight cheaper to run.
Was trying to put together a system cheaper than buying a modern console with the same sort of performance. I think I broke about even with the retail price, but I'll get 17.5% of that back in April
Gotta love tax-back.