Arent cards lmited to 20mbs any way? so 20x4=80 of the usbs 480mbs am i Wrong? I am using a macbook so firewire will work
No. You're confusing megabytes and megabits.
1 byte = 8 bits.
Plus, you're mixing theoretical and real-world numbers.
USB is 480megabits/sec (mbs) in theory. That's 60Megabytes/sec (MB/sec) in theory. USB is about 25 Megabytes/sec in practice.
Firewire is 400megabits/sec and 50Megabytes/sec in theory. But in practice, around 35MB/sec.
(Yes, for actually doing work, Firewire is faster than USB2. Though, I don't think I've actually seen a firewire SD card reader. So that might not be an option.)
Your SD cards have a maximum of about 22 MB/s unless you have the weird Sandisk Extreme IIIs with the 30MB/s read speed... which also only work if you have a special reader since that's not standard.
So with 1 USB port (25MB/s), you'll be able to handle 1 card. (22MB/s)
What I haven't tried, is importing from 2 cards at the same time from 2 ports. That might be your best bet.
Finally, one other thing to find out is if your reader is no good. Many of the early USB2 readers didn't function at full speed. So finding a good reader might increase your import speed.