Maximum current or maximum voltage is rarely maximum power !! That's the huge advantage of an MPPT controller, and there is also a big
difference in their efficiencies, depending on which one (or more) of the "scan" profiles they use. A 20-30% increase is well expected.
IF the cells specify 1C max, I'd definitely try to keep it at that. You will get some lifetime degradation otherwise, but it is impossible to tell unless
you deliberately run the tests yourself. Usually there's a current limit setting on the MPPT?
As for shading .. the "better" brand panels have bypass diodes fitted, which "drop-out" poorly performing sections, but there is a slight penalty
to pay when you do this. When we make up our panels, we break the area down into sections, with a separate MPPT for each.
BUT, without bypass diodes, make SURE NONE of the panel has shade spots. It's the MOST COMMON error in installations.