It might be worth a try with flubit.com, I was a bit skeptical about them but used them one time and got a little HTPC that was £110 at ebuyer for £80 from them, I'm not sure all the sites they match but it might be worth be worth throwing some links at them and seeing what they come back with.
If my experience was anything to go by I'd say ignore their first offer then they come back with a better one, my saving went up by 50% by ignoring the first offer they sent me.
Stammie - Flubit wouldn't accept a few of the links I tried from Microsoft, PC World etc. I've ended up giving it one from John Lewis which isn't the cheapest I've seen. It says it will get back to me with up to 15% saving. Thanks
Flubit was rubbish offering a 1% saving. Worth a go though!
Also, further research shows that the core model would actually be a good by. The heaviest thing I'd do is Photoshop which it can easily handle I'm told.
It doesn't say anything about restricting to only one discount... so it should work
Microsoft have been a funny one for me with Quidco though. When I bought my Surface it worked out about £30 cashback, but for some reason it went through twice! So I received £60 back which was good. However with my Band, because I ordered two sizes for testing, and sent back the one that didn't fit... they cancelled my cashback which I felt was a little unfair