Ideal buffer size

Hi guys,

I’m about to purchase Nuendo live to pair with our new X32, but this question popped in my mind;

What is the ideal buffer size for this combo?

I’ll run it on a HP 4520s laptop
I5 cpu M460 2.53 GHz 2.53 GHz
4 GB ram
W7 Pro sp1
I’ll record to external HD USB 2.0 / 7200 rpm drive
32 tracks

Looking forward to hear comments