Dustin,
I have no experience with, nor have I ever seen a CZ mk300 in person, but there are a few good things. CZ makes quite a few of the models marketed under the Air Arms label, so are known for their high quality. If you do decide to buy one, I'd suggest you go through Top Gun as they are a reputable dealer of fine guns and will more than likely stock any of the parts you'll need in the future. From the pictures on Top Gun's website it looks to be a very worthy benchgun as it comes with only needing a 3" wide piece added to the accessory rail (not necessary, but very helpful when trying to keep the gun stabile in the rest), plus could probably be tweeked to meet your needs as you grow into bench rest. And yes, definitely buy the 12fpe FT model as that could suite your needs right up through the HV Class when powered up to the full 16fpe level.
There was no price listed, so keep in mind: if it approaches the $1000 level you might be better off buying an Air Arms S400 MPR-FT, which is also a 12fpe gun, but carries with it a proven history of winning around the world. I have one which I've shot several 250's with in the LV Class when shooting Indoors at 25Y, which means it would of course do the same if used in the HV Class, and my friend Paul Bendix has the same gun which he uses for both LV and HV, and his is a proven winner even when going against much more expensive guns. In fact, he has an Air Arms EV-2, a $2000 gun, that he leaves at home in the gun safe because he likes the MPR better and feels more comfortable when shooting it.
Talk to Boris at Top Gun and he'll help you make your decision, plus you can trust all he has to say as he use to be an AA dealer, so is very familiar with everything they have to offer as well.
Good luck,
Dave Shattuck
