High performance laptop on a budget!

Hello! My previous laptop has just died an ignoble death, and I'm looking to replace it for around (or hopefully less than) 800 pounds.

-I've been looking at laptops with screen sizes of 15-16 inches - I've been informed that 17+ will be somewhat unwieldly, and my last laptop was fine with a 15.3 inch screen.

-I will be using the laptop for gaming (I don't mind not having games run at the maximum settings, but I'd prefer medium settings to low. Will be playing games along the lines of fallout 3, mass effect 2, etc), and I also use photoshop extensively. I will also occasionally use it for watching movies/tv, but outside of games and photoshop, I'll be using it for the internet and word processing.

-The laptop will act as a desktop replacement, effectively - I don't care about weight.

-My previous laptop had issues with battery life (it was down to about 40 minutes before it became utterly defunct) and overheating, so something that has a decent battery life and doesn't overheat easily would be excellent.

-I'd prefer a large amount of storage (all those photoshop documents and save games!), but it's not essential.

-I'd also ideally like this laptop to last longer than my last one, which had its first major breakdown within four months of buying. If it could last for four years or more I'd be very happy.

-I'd prefer not to buy from Acer, as I and my family really haven't had that much luck with them.

-I was looking at Dell and Samsung - was going to go for a studio 15 dell with the i7 processor (I would have been happy with i5, but my father insisted...), but costs racked up so much in the customisation (more storage, better battery, etc) that it went wildly out of budget. Have been looking at the samsung r590 (http://www.samsung.com/uk/consumer/pc-peripherals/noteb...) but I am concerned that it may not have much battery life - would there be a way to upgrade the battery? And is there a reason the samsung is so much cheaper than the dell with much the same specs?

Thank you for your consideration, this decision is driving me up the wall!