My model 60 is built with the same action and it cycles cci standard velocity ammo which is subsonic. Has never failed me due to light loads yet but I haven't tried the super slow stuff.
Most semis won't, but marlin seems to have their shnit together. Remember you can always make it shoot slower ammo more efficiently by polishing the bolt and bearing surfaces with oiled 400 grit wet dry. And even if that fails you can clip off one coil from the spring at a time until it does, but I personally wouldn't clip the spring because regular speed ammo would be a little too much in the recoil force dept and over time could damage the recoil bumper in the rear of the action.
In short... It will cycle ammo as slow as standard velocity, which is subsonic no problem. As you get closer to 1000fps you may have problems overcoming the spring tension. But from experience, the marlins will cycle more types of ammo, more reliably, than any other factory production semi out there. If the marlin won't cycle them... Nothing short of a custom gun specifically tweaked for subsonics will.
For what it's worth, I'd say buy it! My 60 is by a long shot the most accurate semi 22 I have ever seen out of the box an will easily group under 1/2" at 50m with a cheap 4x bushnell banner and cci standard velocity ammo. The model 60s and 795s are well built little guns that defy their price tag BIG TIME!
