Here's a handy 1RM calculator: Predicting One-rep Max
I guess this calculator is kinda the opposite of what you're asking for, sorry. But the table at the bottom should still be useful (~85% for 5 reps... but if you're doing 5 sets, then 80% seems reasonable)
And strength standards: Weightlifting Performance Standards
Exrx.net also has lots of good info on lifting in general.
I would recommend doing some heavy sets with low reps and some lighter sets with higher reps. I don't think one should train only in one rep range. I've been doing reverse pyramids (a few warm up sets, a few sets at max weight, step weight down and increase reps for a few sets) and it's been working great for me. But yes, in general, working with heavier weights will make you stronger than with lighter weights.