Just to add my 2c (probably more 1c) to the discussion. RIght now, with the stock Ubuntu Studio on a clamshell series eeepc I get xruns even with 512 samples (lowlatency kernel, I think).
I’m sure I could improve that with a bit of tweaking… but not sure I want to really do that 
But yeah… just to say that 128 samples already seems like a stellar thing to me!