Mate, a RGV would be a great fun track bike but i think a 400 would be cheaper and as quick if not quicker up top. I love my VJ23 (the rare jap only SP model) but i know what its good at and where a 400 would be better.
If budget is the key then NC30 is a good bet. ZXR's are the quickest but tend to go pop if tuned and head gaskets can be fun. Not saying NC30's arn't perfect but very reliable if difficult and expensive to tune.
have a look at
www.rgv250.co.uk but dont dare mention a diesel on there unless you like being shot down in flames. I love strokers but they have had thier day and i am not one for rose tinted specs even although i still say my RC30 is the best bike i have ever ridden period