Having spent a lot of time at the track over the years my best advice is to consider that you're pushing everything beyond it's design specification and the stresses involved will reveal problems you never thought of. Once you get onto slicks you cross a line that many road cars struggle to cope with and your conversations need to be with other racers because guys with street cars wont have dealt with the challenges that racing throws up. As you further develop the car to make it faster and/or solve problems the higher stresses will reveal new problems. You'll feel like you're constantly chasing your tail because it's one thing after another. If you don't draw a line somewhere it will get hideously expensive.
That's a long winded way of saying that if there are no faults in your brakes you have probably reached a limit. That limit may not be the brakes themselves, it may be due to flex in the caliper mount or even in the hub, in which case a brake upgrade would make things worse. Not saying you definitely have a flex issue, but it's something to consider.
To illustrate this point, look at these contrasting pics of a Commodore hub, one from a road car and one from a race car:
You're probably a bit of a pioneer because there aren't many (if any) other privateers driving a 3MPS at the same level as you so there is no body of knowledge to tap into. If you can manage the pad wear issue by rotating the pads that will be the cheapest and easiest solution, or maybe the guys at GSL will chip in with a simple solution. Regardless of that, if you decide to develop the car more, have a think about all the other weaknesses you might reveal.