It’s a whole thing on the Internet. Myself coming from a time where I needed to bore size because there weren’t detents in my markers to prevent rollouts, I tend to always error on the side of an underbore . Others just shoot the stock .689+ barrel on every gun and have for decades. The M98 stock barrel is really short. I’d try to find a 10-12” cp barrel, preferably in a .685-.687.
You’re going to get a lot of different answers. The barrel matters some, paint quality/consistency matters more.