well £2.5 k will either buy you a good, clean, low miles gen 1 thou, or a fairly rough higher miles gen 2 thou. If you want the same sort of level of comfort as the 600, then the gen 1 thou is for you. if you want something a bit sportier then the gen 2 is the way to go.
For information the gen 1 ran upto 2005, gen 2 was post 2005.
IMHO it would be better to buy from a forum member if possible, odds are they will know about any foibles specific to the bike and will have cared for it (the EXUP valve needs fairly regular maintenance for example), plus it may have a few choice extras which add to the bike (for example the R6 shock mod, full monty carb mod, exhaust, air filter etc etc).
Alternatively buy a standard one from a dealer/private and then tweak it as you like.