Did I miss something? When did you get a .327 GP100?
As others have said... there's only one way to find out.
We can theorize all day about fouling, accuracy, gas cutting, throat erosion, and obturation; but you'll never know for sure, unless you try it.
Cornbush, for example, has a 7.7x58mm Type 99 Arisaka that was given to him by our grandfather. While our grandfather was secretly building the Arisaka for him, he also worked up a couple loads with .308" bullets, that were shooting sub-MoA at 100 yards.
After we experimented with quite a few .311", .312", and .313" bullets, with mediocre results, Cornbush slugged the bore. It was .314".
...A .314" bore that doesn't like .32 caliber projectiles, but shoots .308" like crazy. And, it doesn't cause excessive fouling.
I've had mixed results with my M38 Mosin. My initial tests with .308" and .310" bullets were rather abysmal (minute-of-mountain-side). But some more recent tests have shown decent accuracy potential (still developing the loads).
I think a big part of it with these rifles may be the deep grooves, though. My M38 slugs at .301" bore / .315" grooves. Cornbush's Arisaka (I believe) slugs at .302" bore / .314" grooves. The tall lands still engrave the bullet very well, and might be causing enough jacket deformation (not really obturation) to seal the grooves. We've never been able to recover one in good enough condition to take accurate enough measurements, to know for sure.
I suspect that trying the same thing in a firearm with shallow rifling would result in terrible accuracy. My .444 Marlin Handi-Rifle, for example, does not have a true micro-groove barrel, but it slugs at .428" bore / .432" grooves. Shooting even .429" bullets leaves obvious signs of the bullet slipping on and skipping over the lands. (though, I've never done formal accuracy testing, to see just how much it is affected)
The grooves in the GP100 should be deep enough to at least make it worth trying.
I've really been wanting to get out with my own .327 GP100 lately. Maybe I should go fondle it for a while...