I've fired several hundred PMC X-Tac 5.56 62gr rounds through my Rem 700 VTR chambered for .223. I did a lot of research on this before actually shooting them. The main problems mentioned were throat wear and chamber pressure. The rem 700 can definitely handle the pressure of a 5.56 round; and I had one problem: 62gr w/ the VTR 1:9 twist was not the best for accuracy. Other than that, it worked perfectly fine.
The most accurate round (IMHO) through the 1:9 barrel of the .223 VTR is a 40gr VMax. Specifically, Fiocci factory 40gr VMax .223 rounds in a 50 count box that cost $20—cant beat that! I also hand loaded several different weights, powders, and powder charges. 40gr was always consistant at 100 and 200 yards. I had a good load developed for the 55gr VMax but I dont have the info next to me. PM me if interested and I'll get it for you...if you are handloading at all.