The 3MA is basically restricted by the pipes, and to a lesser degree the airbox intakes. With decent pipes and alot of careful setting up (when derestricted the 3MA needs big carburation changes unlike the MC18) you'll get around 57-60hp (ish), maybe a bit more if you know what you're doing.

Because of the sensitive nature of the carburation (even straight from the factory) they gained a reputation of being unreliable (not to mention they can also eat ring pegs unless you change the pistons every 7000 miles or so), and if you don't feel confidant in jetting a two stroke, you have to be aware it will destroy itself pretty quickly if you get it wrong. Whilst the 3MA is in fact my favourite race rep 250, I'm not sure I'd recommend one to everyone.

Oh, and they need a bit of work to make them handle nicely aswell...

In other words, the MC18 is the easier option if you want full power and decent handling without doing alot of work.