Right, so I visited two more bike shops in London to test out some more bikes, one of which was Evans (thanks Dheorl).
Rode a Specialized Rockhopper (again), Genesis, Kona, Felt Q720 and Trek 6000.
The
Rockhopper,
Felt Q720 and
Trek 6000 were the best. One thing I've realised is that the SLX rear mech shifts MUCH cleaner than a Deore or anything lower. The brakes on the Trek were particularly good, but the handlebars were too high above the fork (though that can be adjusted). Also, the 6000 is slightly below my price range, so they're willing to order in a 6300 to try out.
Not all the bikes were in my size, and they're ordering in the Felt and Specialized in 21" for me to try out by the end of this week. The Felt felt really good, and is reduced to £600 from £700.
A lot depends on the type of riding you are planning on. The big-ticket items (frame and fork) will make the most difference. You might also consider getting a bike with a decent frame but a very basic lowend fork (like the Dart series), spend some time riding to see what you like and don't like, then replace the fork with something suited specifically to your needs.
As is stands, all three of the above I would consider buying.
One thing I realised was that all the bikes in this price point have pretty bad forks, Darts or, at the absolute max, Toras. The problem is that they are extremely expensive to replace (Fox forks are like £500+) and I am REALLY tempted to buy a
Focus Black Forest and get a Fox fork... which is like worth over half of the price of the bike itself.
So I'm torn between buying at a store and being able to test it out, or buying the Focus and getting high-end components for really cheap. I know I'm not going to be able to afford a £500 fork anytime soon as I'm a student. How much of a difference on the trails will a good fork make? I suppose it's a stupid question. Will the Dart feel crap? I'm not going to get to test them out on the trails and all the forks feel similar on road.
Decisions decisions.