I would just perform progressively heavier sets to see where my strength is at. I would just stop a predetermined number of reps each set until you reach the heaviest set and go to failure. Also, how many reps where you hitting with the 100lb dumbbells on each angle?
Incline dumbbell Press 50x20, 60x15, 70x12, 80x12, 90x12, 100x14 failure
I wouldn't just jump straight to the 100lb dumbbells. Don't worry about strength, because if you did lose any it shouldn't be much and you'll gain it back quickly...
Anything worth having is never easy to achieve.