Since you said the shoot at 200 yards, I'm going to assume you're talking about the CMP GSM Vintage Rifle matches (which include Garand matches).
The target used in these matches is the the NRA 200 yard target. You'll find the X-10 ring on that target 7 inches in diameter. Thats 3.5 MOA.
Very few Garands out there that can't shoot 3 MOA. so I'd say the Service Grade is more then capable of cleaning the targets.
I got my Garand in the early 80s under the DCM. Then it was a once in a life time deal. You didn't get a choice, you got what they sent you.
Since then I've shot the crap out of my Garand. In matches, and when I use to run sniper schools for the NG using M1C/Ds. Checking my rifle with throat and muzzle gages, by all rights the barrel should be shot out......maybe it is, but it'll still shoot under 3.5 MOA.
If I was in your shoes, I'd get the Service Grade and spend the extra money ammo down range. Concentrate on Off Hand (standing). These matches are won and lost in the standing position. 1/3 of your score.
Regardless of which rifle you get, spend hours upon hours dry firing in the standing position.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071