Host processors...again

I'm trying to wrap my head around settings on my system. In my little project studio I'm using PT 10.3.9 with an HP ProBook 4540s i7-3612QM 2.10 GHz 8 gig RAM 64-bit Win 7. Under Playback Engine my drop down for host processors shows 8. I'm seeing discussion that a rule of thumb is to use 1 less than total, but I've also seen reference that more than 4 showing may be deceiving. So should I exercise my "rule of thumb" here with 3 or 7? I fully understand not one size fits all, but if the answer is definitive to not acknowledge processors 5-8 I'd appreciate the guidance. Thanks.