You won't feel a perceptible difference in speed. The jump from a 130mb/s sequential reads traditional hard drive to a 450mb/s solid-state is already apparent enough with the majority of those perceptible improvements coming from day-to-day seek time. So unless you absolutely crave that you want the best the consumer SSD has to offer or need something else -- like warranty support, I'll always recommend budget SSD over their more expensive counterparts because you get more size for a slight dent in speed.

The Extreme will be too expensive. That's roughly Samsung PRO SSD territory.

Stick with the 128GB. Unless you need the added space, 128GB is the sweet spot right now. And in the case you need a bigger capacity drive in the future, you can always purchase them once prices goes down over time.