Hello! Yeah, I have try to launch some different playload this morning. The OLS II ER rocket can launch 70 tons of playload in lower kerbin orbit (LKO) no, more... With 90tons for exemple, the rocket cannot made an orbit, but with 70 we are at the limit.
To launch 70t you must change the size of the fairing in the top of the lifter of course. You can launch, crew vehicles, probes, rovers, fuel, etc...
All the best,
Nuno Seletti