I agree Fishhead, but as yourself being a vet of the pen-to-pad art, FH are you speaking generally of sharper/larger players being "very successful" in both cases, or certain players from all strata?
DougJ, I seem to find your dilemma of "The hard part for me is determining an expected win percentage on each bet", in my case(and most people that I've seen), it's more a case of ranking one's play volume & play size most proportionate to areas of personal strengths(best sports, totals, playoffs), as the best way to achieve better results.
And generally have found that volume/board play is only mastered by BMS, Middlers, Movers, and Pros with plenty of help(smart marks/connections)..as there is just so much ground to cover, from capping to chasing quality numbers(early capper or lottery regular?) to watching DB ad nauseum, in order to be extremely successful long term.
I prefer college football & college hoops, NFL, then MLB in order(it used to be the king money making sport..now game's changed..still of quality..just not as Kosher!), with NBA and NHL reduced of late years to playoffs only, and horses mainly just a Derby & Breeder's Cup pursuit..best left to touts & movers!
If one had BW's wallet & college capping network, BB's NFL/NBA plays & halftime skills, HH's foots & hoops & boxing plays, PokerChip's punch plays, Orlando Larry's NFL, Lunatic's 25 college football plays each week,etc..then "MAYBE" board action & Vig wouldn't maim?
Unlike the whale or a pro, the average player's play size can generally always be accomodated playing their better plays tiered without a cap, where as the high-roller has daily battles to get down or fill up proportionate to their play size at desired numbers, and get shut out daily when shopping after the move..thus play at bad number or pass.
Less & Larger is better, if you can rank and file 'em well!