Getting back to Mike's C130....

Mike, you need two things to get up to speed and climb.

You need enough RPM and pitch to reach speeds the model will fly at comfortably. And you are right that on a large and fairly draggy model like a C130 that the model will not reach the actual pitch x RPM airspeed other than in a dive of some sort. So finding the speeds you expect to need to fly at for stall, cruise and max speed then proping and powering for a pitch x RPM that is about 20% higher at full throttle than your desired maximum level speed is good.

Your thrust rig being used to test for static thrust is misleading you. A 12 inch pitch prop is operating at a stalled condition when running static. And that means it sucks current like crazy. Far more than it will in the air at a reasonable speed. So during the takeoff run it will reach a speed where it stops being stalled. When that occurs the RPM will pick up and the current will actually drop. So for flying and climbing at a reasonable cruise speed in the climb you can expect more from each motor and prop than your testing indicates.

To lift off and actually climb you are way over powered for a scale like lift off and climb angle. You could achieve a scale lift off and climb angle with more like a thrust value that is down around 60% of the model weight. And even that would likely still be a higher thrust to weight ratio than the full size Herc when loaded. So even with your "lower power" setup you'll likely find yourself only using part throttle for a nice scale like takeoff. Full power takeoffs even with your lower cell count packs will resemble a hot fighter sort of takeoff. Or the takeoff of the real thing when unloaded and doing one of their impressive air show short liftoffs.

The only question now is if the 12 inch pitch and RPM that your pack voltage turns it at is a good match up for pitch speed to the speed the model will need. You want the prop to un-stall at a speed low enough that it will occur during the take off acceleration. But not TOO early or you might run out of top end pitch speed. I'm not familiar with the electric propulsion software out there. But one or more of these analysis and prediction packages might be able to tell you that sort of information. I do believe that most of them also will give you a good estimation on the stall speed. And given the cost and time in a project of this sort it might be worth looking into buying Motocalc or similar.

The big numbers like your Herc always look so intimidating to me. I don't work with that size model. My first thought was that this thing is way heavy. But then I stop and think about the large scale sailplanes that are up around that span which weigh in at around 20 to 25 lbs. And you'll have a lot more wing area because of the aspect ratio difference. Suddenly 55lbs doesn't seem so bad. You sure won't hit the "scale" stall speed by a long stretch. But I'm thinking that it might just look rather scale like anyway. Good luck with it.