So why don't I just get the 980? Is it better than the R9 290?
Because while it is faster, it is not going to be a big enough upgrade from the 290 for the amount of money you will be spending. While Nvidia called the 900 series "new gen" card, performance wise it still belong in the same gen as the 290/290x/780/780Ti.
Sure you can go grab a 980 now, but that would also mean you will be missing out of the opportunity to play with the 20nm true next gen big maxwell when they are out...unless of course, you don't might spending another £550-£600 again on graphic card.
Just as I mention before, while the 980 is faster than the 290, with a 8350...you simply won't benefit from the upgrade due to the CPU bottleneck. Regardless of you graphic card upgrade decision, you cannot go wrong with upgrading from the AMD CPU to Intel CPU and platform first.
Just to make it clear, all my suggestion for you is regardless the graphic upgrade is base on respecting your wish to switch to Nvidia, and I have not intention or trying to get you to stay with AMD or go with AMD again in anyway. All I'm saying is that...if you spend £430-£450 now getting a GTX980, yes you will have a graphic card that's more efficient, and around 10-15% faster than the 290; but if you spend £550 on the mainstream big Maxwell in say may be 6-9 months time, you'd have a card most likely 50% or more faster than the 290, AND even more efficient than the 980 due to the process move from 28nm to 20nm.
Another thing worth considering is that I don't know if you have any plan for 4K gaming in the future, but for cards at the moment, you need three of them to game at 4K comfortably...yet the SLI scaling is quite poor for the 3rd card. If you go for a big-Maxwell card, it would probably be able to provide enough grunt for 4K gaming with just 2 cards, so poor SLI scaling for the 3rd card wouldn't an issue.