350 for just a base unit… Including an OS or excluding?
Given you want to use Photoshop and do home video editing, 2 applications that processor power really makes a difference, 350 quid for the box won’t net you anything serious I’m afraid. Granted, it will be a fair whack quicker than what you’ve got already, but spend more and get more power would be my advice if you’re at all serious about it’s performance.
If it’s all just casual use, and you just want something a bit quicker than before, (I’m assuming you don’t want to build yourself?), take a look at the following…
http://www.ebuyer.com/product/271630
That would be a good start, under budget. Maybe spend £40 on a GFX card to go inside it to help with HD videos etc (I’m assuming you’re not gonna play games on it)…
If you can stretch the budget though, have a look at the following…
http://www.ebuyer.com/product/264251
Over budget yeah (and still no separate GFX card), but that’s the kind of processing power that’s gonna last you a good few years at least for photo and video editing and the like.
Or build your own!