The standard bak-pak really isn't for tanks bigger than 55gallons. I mean, it'll work but it may not skim every last bit out, unless the 75 is understocked.
And no, the pump on any skimmer does not count towards your total circulation, because that pump is only running inside the skimmer. Especially with CPR's...your pump is pulling water AND air...and the air really slows down the water intake. an MJ 1200 is something like 295gph, but when it runs a skimmer, you're probably at 150gph, and that's just the intake. The water churns inside the skimmer, and flows out into the tank at probably 60gph.
Former advisor and planted tank geek...life's moved on though.