Only 3 weeks ago, I picked up a Compaq Presario CQ61-425 off Dabs.com for £317 less Quidco (£10 off plus 3% cashback). It's got 2.2 Ghz Processor, 2GB RAM, 160GB HDD and came with Windows 7 Home Premium edition. 15.6" screen.
This is the same model but now listed at £359.59
I know this is at the bottom end of the specs you're looking at but at least you have something around the £300 -£350 mark to benchmark against. As you say, there is a lot of choice!
If you do go for dabs.com, don't forget to heck out Quidco for any vouchers as well as % cashback.
Let us know how you get on with your searching!