Guitar Hero II or III???? for PS2

Ok I have an old PS2 and don't play much at all. I play mostly PC games as I won't get a new console because I do not have an HD tv. I don't watch much TV so there is no need for it. But I liked guitar hero on the 360 at a friend on mines house. I saw it for PS2 at GameStop. I have a $50 card for that store and went to pick it up the other day for $80. The girl said Guitar Hero III was coming out in a few weeks, is $10 more, and comes with a wireless guitar and has an extra button. So my question is how true is this? what do you think GH II will drop to after the new release. I just thought it was fun but don't wanted to get the best experience.

handle GH III? I would assume so if they make it for that console, its not like its a PC game where you have to check the specs.