I think I'm running an OS #8 in both of mine at the moment. Haven't had a chance to try the MC-8 in either yet. I do know that running a MC8 in my XTM24.7 changed tune considerably and made it run much better.
Just bought a couple MC8's from my LHS... now I just need to remember where I put them. At $7 a piece, I should pay closer attention to where I lay those.