i need to get closer track side!!

i have my pan GX1 and i have just put my 45-200mm lens up for sale on ebay.
(for anybody interested there is still 8 days remaining)

i used it for no more than 250 shots last weekend at silverstone for the motogp bike races.

i came home with a few good shots from luffield corner. 1 especially of casey stoner but that was by mistake not from expertise.

i found that i got better results from panning instead of oncoming bikes round a corner. i even prefocused on the red & white paint on the bend and never got as good as panning.

so the lens is for sale!

my question is, im considering on either buying 100-300mm lens to get that bit closer or going back to DSLR 550D and buying a 100-400mm is usm on a 12 month interest free deal.

very exspensive i know but i love my bikes and i love silverstone. i am going to world superbikes in august and i want some excellent results.

shall i give the panny 300mm a try first? if no good then sell?

--
Regards

Michael