Originally Posted by 8540tomg 
Hold out for that K 200/2.5. It will be worth the wait. Hope you don't have to wait the 20 years or so I did.
There is just no substitute for speed in the conditions you want to shoot.
I have the K 300/4 as well as the M 400/5.6. I have used the K300/4 with some success in dimly lit school gyms. This lens gets dumped on by some but I submit it is the best bang for the buck in the 300mm manual focus category. Forget the M 400/5.6 as it is just too slow and big for that application. Fine for outdoor work where you have lots of light and room but IMO hopeless in an auditorium.
Tom G
200/2.5 - I couldn't wait for one at the $ I had so I went and got the 55-300. At 200 it is @ f4.5, so roughly 1 1/3 stop off. With SR and use of a monopod (can I use SR with a monopod?) Might just be able to do it.
Another thought is possibly the Nikkor 180/2.8.
k300/4 - well compared to 55-300's f5.8 @ 300, another 1+ stops difference. I wish I could see how big it is compared to the 55-300.
I've got the Pentax-A 70-210 as well as the Vivitar Series 1 70-210 f3.5. I'll post the pics soon as I can put em up in flickr.
The 55-300 will have do for a while until I get another opportunity (reasonable one that is) for the 200/2.5 or sensor technology get's better. I figure by the time I can get the 200/2.5