Magdrives don't produce dangerous levels of pressure. Some people like this but honestly the reson I would move to a larger pump would be to get more pressure in hopes of turbulence and not to get more flow rate.
As for whether to go to ever larger pumps, I personally prefer to remove flow restrictions (drill out the fittings and/or move to larger fittings) and use smaller pumps. That way you are dumping less heat into the case, taking up less space, and spending less money on pumps.
With the Maze2 (and I suspect most channel style blocks) there really is no benefit over 1-1.5 GPM of actual flow. Take a look at this picture (Maze2/heatercore/Eheim 1250 with flow adjusted with ball valve):
Notice that performance hits a minimum and then plateaus. What happens is that you reach a point where water flow is sufficient to minimize the difference between water temp and waterblock temp. Any increase in flow over this point only serves to reduce the effectiveness of your radiator's heat dissipation. If my pump had been large enough, you would see performance actually decrease at really high flow rates due to a combination of the increased heat from the pump and decreasing ability of the radiator to lower water temps.
Huge pumps are for evaporative cooling IMO where you are moving water vertically a goodly distance. FOr an internal setup the 1250 is more than enough pump as long as you have an eye to optimizing flow in the loop.