new rear disks, need more "bite" - any suggestions?

You don't want the rear to lock up before the front. 70% of your braking capacity is in the front.

What tires? They go a long way for braking performance.

What Garry said on the hydraulic side. What size master? Are you running an adjustable proportioning valve?

As you move up in "performance" pads they require more heat to work. So again you have a teeter totter of heat for a performance pad to work over the initial bit but early fade of a general pad.

Did you bed the pads and rotors? As in break them in? this is very important.