The audio world seems to have given up on latencies with buffer sizes any
lower than 256/2. Certainly, most recording can be done at even higher
latencies with external monitoring but the use of softsynths or software
effects that require low latency monitoring from the computer is difficult
at best.
I can use my MOTU USB device at 64/2.
There is also the problem with usb devices that the latency changes every
time the audio device is opened by software.
Apparently now fixed (or certainly much better) in recent kernels.
The computer audio world lost when the audio device manufactures jumped
from firewire to usb. Maybe (but don't hold your breath) something will
change in the future. Or look for a PCIe based audio device like the
audioscience cards.
thunderbird (aka "PCI.? bus on a cable") is presumably the right answer.
but that's just a reminder that the proximal issue here is "what connections does my laptop provide?"