TBH I would go for a 600. A limited 400 would be shit slow, not that a limited 600 is going to set your pants on fire.. but it should have more grunt even if it's limited to 33bhp.
For sub £2k I'd be looking at Kawasaki ZX6r, should get a pretty good J1 or J2 model for that money.. and they are a very capable bike once you de-limit it. You could also look as Honda CBR600 but they will be more money so you won't get as much bike for your cash.
HTH