pipe size for vertical discharge?

for the vertical portion of a sump pump discharge - what's the optimum pipe size for a 4000gph pump (at 10')? wider pipe allows more peak flow, but also presents more static head pressure against the pump, correct? once the discharge hits horizontal or downgrade slope wider is better, correct? the application is a back yard sump to drain the low spot that turns into a large pond during heavy rains. insufficient grade to gravity drain it. will involve pumping up hill about 120', at about 5' elevation change. then downhill 180' at 5' elevation change. plan is to pipe 1.5" uphill then change to 3" pvc for the downhill run, with a cleanout at the transition. I thought about going 2" for the uphill run, but am concerned that will slow down the pump due to excess back pressure.