I converted the Raiders to a 3-4 principally because I had cap problems and good LB are far cheaper than even sucky DT/DE.
Sending different numbers of players does affect sack totals some, but as has been mentioned, because there are no double teams, you don't get as many sacks as you would think.
But you do get favorable results depending on the quarterbacks. If I send 5 against Tom Brady, I pay. If I send 5 against a bad QB, there are a lot of bad throws. And more sacks.
But mixing it up appears to lead to more misreading of coverage from what I can tell. I tend to mix the number of men rushing rather than switch between zone and man. (When you have Nnamdi Asomugha and Quan Henry, press man is the default coverage)
Also, moderate your expectations! The fact is that DT/NT do not get many sacks.
This year there was one DT/NT with 7 sacks, and another with 6, three with 5, and 3 with 4. (all these stats from
www.profootballfocus.com)
The 4-3 DE with more than 10 sacks this year had 15, 14, 14, 13 and 12 sacks. 3-4 DE was capped at 9.
Brian Orakpo was the only 4-3 OLB with more than 6 sacks (he had 12). And 3-4 DE with more than 10 sacks had 17 14 and 12. That is 9 players with over 10 sacks in the NFL. So if your team does not have one, then it could just not be your player's year to get the really high total.