timing question

Ok here is what I have my MSD 6 went out and they are fixing it. So I plan on useing it on my sbc with the MSD timing copmutor the mechanical advance will be locked out and the fixed curve in the timing control will be used. 20* total advance.
Now to the question with some info. It has a chip adjustable timing retard right now at 4*. My truck cruises at 60 mph at 2000rpm with it empty.
Should I set the retard to ingage at this rpm and do you think mor would help? Full advance on the computor hapens at 3000rpm. Vaccum advance is stock.