Which racquet should I buy?

Personally, if you are going to become a "pro," I'd recommend the Head Radical (the first link). It is heavier than 300 g (it is actually 320 g) but I think that the weight will work out, as several pros use heavier. Honestly, it all depends on which racquet you will be comfortable using. If you could try these out before buying it, I would recommend doing that. Personally, I use Babolat (but not the listed link) and I love it. However, the racquet you have listed is fairly old. I would use the Head Radical, it is of course used by the best...Andre Agassi (well at least a version of the racquet).