As others have said, if you are not racing yet, then get something robust that will handle training as well as racing application. I would look at getting something handbuilt to your specific requirements. You will not really know what those are until you have been racing for a while, so why don't you get a set of Fulcrum 5's to begin with, and start racing on those.
For sure the wheels will not be the thing that helps/prevents you from doing well in Cat 4 races. Spending a £1000 on bling to reward yourself for a good result once you have achieved it, is a lot nicer than spending the same and then discovering that you are not competitive and racing isn't really your thing.
Having said that, if you are determined to spend now, hell it's your own cash, take a look at these guys options:
http://www.stradawheels.co.uk/shop/
http://www.wheelsmith.co.uk/wheelprices.htm
Personally, I got a bit of a thing going for those Ambrosio tubs on Chris King hubs, but you really have to choose something that will appeal to YOU on a style level, because you will struggle to see the performance improvement of £1000 wheelset over a £300 one until you get further up the racing foodchain.