If you want to race get either one. If you want to win get a 450.
We have a class called sponsors cup which has atva pro riders in it. One being Mark Madl and the other being Devin Heimes. Devin started this season on a built to the max best of everything 250r with a 265 kit in it and could not beat the 450's. He was class champion 2 years ago on an LTR450 and 2nd last year. Now he is back on a 450 and competing for the win each week. Trust me if they could win everyone would race one becuase its no secret they are cheaper than a 450 motor. Also most track will only allow up to 265cc 2stroke against the 450's. you can pick up a trx450 for about $2k right now.
Also most guys say get the 04-05 but it is not as fast as the 06-07. You can find 06 with kick start also. However the 06/7 models have higher compression, the FCR carb, longer swing arm. Get an 06, put a full HRC kit in it, do the green wire mod, add a pipe and k&n filter setup and you will compete very well. However I would get suspension first then the mods. You will be faster with good suspension and plenty of Hondas getting parted out all over the web.
Trust me it won't compete in MX, now TT racing different story.