I'm considering ponying up for the 200mm f/2 VR + TC 14E II instead of the 300mm f/2.8 VR.
My reasoning for this is that it'd be more flexible: you'd have a razor sharp 200mm lens with outstanding subject isolation and low light capabilities and, when bolting on the TC, you'd have a 280mm effective f/2.8 telephoto - perhaps not quite as sharp as the 300 f/2.8 (and with slightly less reach) but still capable of delivering the goods.
The 200 f/2 and TC 14E-II can be had for around £2800; about £200 less than the 300 f/2.8
I've tried the 300mm and it's a cracking lens alright but, personally speaking, I'd have select limited uses for that focal length, though it would be indispensible at concert shoots where I'm restricted to shooting from the rear of the house at the mixing desk position... but only if I could pair it with a 400mm f/2.8 as well
