I would expect that given the same dur @ 0.050" on both cams, the higher vacuum reading on the roller would stem from the fact that the advertised duration would be shorter...so literally, the valve is off it's seat for a shorter amount of time given that the roller lobe ramps are usually more aggresive than the flat tappet ones.

In my case I hope for a better throttle signal (i.e. higher vacuum), but since the roller cam actually has a longer adv. duration any such increases would have to come from the bigger cubic inches and the 112LSA...or so goes my thinking at the moment...ha ha...!