Waldo is not correct. The performance is based on the assumed calculated temp. This sould clear all obstacles. You can however always select full thrust if desired, but not necessary.
i,am not sure for 757 but on (at least our) 737 we have a 10min thrust limit once SE If you use full thrust then it's only alowed for max 10 minutes. so our normal ops is after cleanup to selct Max Cont. Thrust (MCT) to continue the climb.
Only in special cases you could run into the 10min max. When making a SE-go-around with a very high accelaration segment you could run into the time limit.