bor0101, I'm gonna be honest with you. Whether you've figured it out or not, you already don't have a good rep on this board. But you asked a normal question, that some people also might want to be asking, so maybe some people will respond.
PLC Juniors, for me, was NOT fun. I did, however, miss it somewhat when it was over. Its weird, but I believe that most Marines can agree with me on this due the fact that you know that you've been changed so much. I think they've changed PLC Juniors since i went...but anyway. You don't shoot stuff, you use blanks. You don't start live fire until TBS. You get to ride in a helicopter once, if you're lucky, and thats the end of PLC Seniors before the Crucible. (Don't have that anymore do they...) You do learn and do Marine Corps/military related things in the field that are awesome. But at the time, they put you through so much stress that you don't enjoy it while you're doing it. The whole point of it is to weed out the people who want to be there for the money, the girls, their father, or because they just think its cool from the people that really want to be Marines. They do this by stressing you out and putting you though lots of physical events. If you want to be there and succeed, and you are physically fit, you'll finish. By the way, you say you run a 300 PFT already, I think your idea of a 300 PFT may be drastically different than a Marines, but who knows. Anyway, most physical activities at PLC will be in boots and utilities with some sort of back on your back and a rifle in your hands. Its a little different.
This isn't really a well thought out answer as you can tell. I too was a science major, so maybe i can blame it on that right. But its a start for you and maybe some other people will add some other things. Bottom line bor0101, you need to really reconsider joining for the reasons you have discussed earlier. Also, you think not going to a recruiter is bad and will take your attention away from school. Man, when i wanted to be a Marine, I wanted to talk to every Marine or person I could who had any information for me. I couldn't find out enough... And I was a physics major so school was an issue. Thats another reason I don't think you are too serious about this.
Good luck though.
And another thing, what the hell kind of response did you think you were going to get by coming on a Marine board and saying you wouldn't mind boxing one of us. COME ON!