The X-treme (and Berry's) 223 FMJ's are just that- Full Metal Jacket, even though they are both sold by companies that sell lots of "plated" handgun bullets.
So they can be loaded to normal jacketed bullet rifle velocities. I'm using the X-treme 55 gr FMJ BT w/ cannelure for range/practice rounds, with 24.7 gr Hodgdon H335 or 26-26.5 gr CFE 223 powder for about 2,850 fps out of an AR w/ 16 inch 1in9 twist barrel. PMC / Federal / LC brass. Trimmed to 1.752" CCI #41 primers and 2.220-2.225 OAL. Light crimp with Lee FCD. (Some LC brass may require a couple tenths more powder, due to larger case capacity to get same velocity).
The recipe above cycles my gun fine, seems pretty accurate, and is not overly "hot". It's within published load data on Hodgdon's site, although they use the Sierra 55gr SP and of course don't list these bullets.
If you stay within published powder/load guidelines, there should be no problem pushing these over 3,000 fps and depending on barrel length, even higher...