Others will correct me if I am wrong but I would think cruising around at cruise speed most of the day at 3/4 up is too far. Interested to see what others think.
Wesley
The trim limit switch protects you from putting the outdrive too far up thereby putting unnecessary strain on the driveline and the u-joints in particular. Mercury has designed that out drive so if necessary you can run with the outdrive tilted as far up as the trim limit will allow. Keep in mind though that each boat hull will respond differently to trim. My 260DA requires almost full trim (to the limit) to plane smoothly in what I call the "sweet spot" where you get the best speed out of the boat at any given RPM. My 240SD on the other hand required very little trim to get to the sweet spot and in fact if you put the drive up to far it would cavitate (or suck air rather than water) and cause the engine to over-rev.
Everyone should find that "sweet spot" for their boat and whether that means the drive is trimmed just a tad or most of the way to the trim limit then thats where you should run it for your boat. Loads (or how many people are in the boat) may affect that a bit but generally speaking the amount of trim you need for cruising along remains the same regardless.