Macbook + Logic 8

1. I'm getting a new mac notebook mainly for using Logic 8. Do you think I should go for the 2,0 or the 2,4 ghz model?

2. How much difference will I notice? I think I'll be using up to like 30 tracks at most, with standard effects and some software synths.

3. Is there more latency with USB-audio interfaces then with FW?

4. I'm using a line 6 ux2 right now (usb) works fine, but I'm thinking of upgrading to something with more I/O's. How many channels can I use with usb?


Thanks in advance!