Nobody can answer that question for you. Only if you try it out yourself, you will find out. The best Barton chips can get to 2.3GHz on air, or even 2.4GHz if you are lucky. On the other hand, if I had to guess I would say that maybe not even 2.2GHz are possible on your 2800+ because it probably couldn't reach those speeds at AMD fab and that why it was called 2800+, and not 3000+ or 3200+. Of course I am only guessing here so as I said earlier, only if you test your CPU, you will find out its limits.