MSI Radeon R9 290 4GB or AMD Sapphire R9 280x Dual-X Radeon 3GB? I've heard that the 290s overheat often is this true? The 290 is about £40 more then the 280x.
The 290 is a vastly better GPU than the 280x which, subsequently, is just a rebranded 7970. The 290/x overheating issue is only with regards to the reference cooler, as long as you get a non reference card, you won't have any problems.