I have a 350 and it is an awesome weapon once you break it in, and get used to how to hold it. If I had to do it over again, I'd probably buy a tuned B gun from Mike as I use it for hunting. My biggest fear with the 350 is dinging up the stock in some horrible fashion. Since I have almost $500 in it, keeping it looking nice is important to me.
The other thing you might want to do, is there seems to be a lot of 350s for sale used. You may even look there and use the saving for getting one of these dudes to tune it for you.
For some reason I think I want another magnum. I'm saving my $$ of a TF 89. I have a "gun can" that I drop all my change in, birthday money, etc into. I'm torn between it and just going for a R-9 clone tuned from Mike (which I know isn't a magnum, but I've heard good things about the gun).
Right now my problem with my 350 is that I'm loathe to shoot it around my neighbors. I didn't realize how loud it was until one of them said something to me one day (he was cool, he just said it sounded like I was shooting a .22 in my backyard). Now I'll go out and snipe a squirrel with it, but I don't target practice it at my house anymore. For that I shoot my Whisper (if I want to hit) or my Air Hawk (for plinking cans).