Here is a link to the factory WSSM data for the .223 and 243 WSSM's. Some say that the 100 gr 6MM load is slow.

www.shortmags.org/shortmags/forum/showthread.asp?topic=14&thread=214

I get the 55gr. figures with my .243 winchester and 22" barrel! It outdoes the .243 by only about 100 fps with the 100 gr. This an improvement because... My .243 is already a short action. I like it, I'll keep it.
Yardbird