Sounds like you have a plan laid out. Good for you! And to your mention of having some extra weight right now, hey man....most of us do. Depending on your actual size, I can see where a Gas Gas 200 might be a little under powered in some situations there in the mountains of east TN
I know you didn't ask for a sermon, so I'll give you my personal feelings about the 300's.
You cannot go wrong with a Gas Gas 300, of any year. The power is smooth, predictable, and the handling is like nothing else I've ever ridden in my 40+ years of twisting a throttle. Engine reliability is unreal. But be careful when you test ride one, especially if you just got off an orange 300. Your first impressions will be "Man is this thing slow or what?" No...its not slow by any means. It simply has a trials torque feel (usable power) that can be very misleading. Put the bike in the woods before coming to any conclusions. The worst the conditions, the better this bike works.
My first Gas Gas experience? After leaving the orange company, I bought a new 2010 EC300 sight unseen because the dealer had to order it. Heck, I had never ridden a Gasser before but I had to see what I had been missing.
My first trip thru the gears....I stopped and actually looked at the stickers on the bike to make sure I had picked up a 300. It was NOTHING like the orange bike I had previously been racing. To be honest, I was very disappointed at the lack of hit, but still loaded the bike up and headed to a local hare scramble the next day. After one lap, my "buyers remorse" turned into complete excitement about the bike and how well it worked in its element. Not only was I pumped, but so was a good friend at the time, who rode my bike, then made some drastic changes in his life path afterwards. (Nuff said)
Long story short....my passion for this brand doesn't come because it's my job. It's because I feel it's THE best all round off-road 2 stroke out there PERIOD. Is it perfect? No, but none of them are. The 300 Gasser has a little buzz in the bars that takes some time to get used to. (why on earth did the factory stopped using a head stay is beyond me) and feels porkier to me than the 250 for some reason. Another slight aggravation with the new frames (2012 and newer) is not having a large capacity fuel tank available. Most average skill riders don't have an issue with the stocker, but for the A class racer or the long distance trail rider, we need a larger tank.
That's about it on the 300 IMO but...for me...if I had to pick between the 300 and the 250??? I'll take the 250. I have simply fallen in love with it this year. I feel MUCH faster on it than the 300, and allot less tired at the end of the day.
Beta...I have no comment because I've never ridden one, but I have several friends that are have taken the plunge, and they remark how similar it is to the Gasser in terms of power. The GG handles better they say, but the Beta steers sharper. I have no doubts it would be a good choice as well.
Sorry to drag on and on. Let me know if you want to get together and ride. I'm not that far from you. Perhaps we could get together with Ken (Gasser) for a ride somewhere.