Looks like I m bringing this one back from the dead. It may sound crazy but I'm in with the M305 crowd and for several reasons....
1. The opportunity to shoot service rifle is fleeting and the very few times you will have to shoot your AR15 annually may make owning one tortuous (like it was for me). Lovely rifles indeed but very expensive to own considering the very few opportunities to run and gun with them. If your situation is different than mine then disregard.
2. M305 in tuned and bedded condition will run you $800. Still the best value for a semi auto battle rifle in Canada, in a calibre that will print at 500m no problem.
3. Will you win SR matches with this rifle? Unlikely, the AR has the edge... Sufficiently so where the shooter is at a disadvantage regardless of his or her skills. However what it comes down to is your own personal expectations of yourself. If winning at any cost is more important to you then run a slicked up AR15. If you want a real world rifle you can take with you anywhere and do anything with then choose to excell with the M305. Being really good with one rifle has serious real world advantages.
4. I've shot SR with Enfields and AR15 rifles. Of course I. Prefer the AR15 however my compromise is the M305. And anyways.... Real men don't shoot rifles in a calibre less than 308" dia. Lol
5. 7.62x51 is more available now than it has been for the last decade. The norinco ammo shoots very good and is very affordable. Easy to get components for and reload if match ammo is your forte.....
cost benefit fit analysis for me is a slicked up M305.
However if you want one rifle specifically to shoot service rifle and have $3000 to $4000 available go with a 20" AR15 (1/7 twist if you can get it and intend to shoot 62 - 77gr bullets) otherwise 1/9 for 55 gr is fine to

. The dollar amounts may seem high but if you factor in practice ammo, optics, mags, chest rig and a few simple accessories it adds up pretty quick.