I guess it just depends whether you are doing track days with the sole intention of racing or not really.
Im over 6ft and 14.5 stone. I bought my gsxr600 simply to enjoy track days - and its working a treat. The bike is quite tall (so comfy) and 600cc is plenty of power to get me into and out of trouble!!
If I got good enough to consider racing I'd have a re-think and would probably sell the bike for something a bit better - or a class not quite as full on as 600s. But for now thats a far away thought - Its just fun fun fun!!