If i were you i would stick with Beta. last year my gasser txt 125 2000 had a lot of problems. i ended up having to re build the whole new backwheel because the hub cracked in half! Now i have a Beta 06, and the fact that it may be a bit heavier than a GasGas is not an issue, as i find i am improving much quicker than i would have done on my gasser.
Thats a 2000 model if your going to get a gasser at least get a recent model not saying they are alot better than the txts cos they were bullet proof but the newer pros 04- 06 seem to be mint.