Go with the 180 size rear - there are lots more choices in tires with a 180 than a 170. You can alter the geometry to quicken the stearing simply by raising the rear or dropping the front. With the larger contact patch a 180 should be more stable and drive out of corners better as well.
My recomendation is to make a firm decision on tire brand and stick with the same tires while you muck around getting the set-up correct. All too often I see guys changing tire brands before they get a baseline of set-up on the bike or not making changes required going from one set to the other. Once you get the set-up correct you can measure the radius of the rim/tire combination and can make changes as needed if you decide to change brands. If you like the feel of your bike now, measure the radius of the front and rear tires you use compare it to the radius of whatever new tires you are going to and make whatever adjustments to the ride height to compensate.
In my opinion Pirelli is pretty good - I went from running Dunlop slicks to the Pirelli DOT Race tires at the end of last year and the Pirelli DOT tires really surprised me with the amount of traction they offered. However, I will note that traction did drop off fairly dramatically towards the end of the second day of racing on the same tires (your mileage my vary but - after 4 practice sessions and 5 sprint races my tires would start to slide more than stick).
The nice thing I found about Pirelli is that the profile of the DOT Race tires and the slicks are close enough that you don't need to adjust the suspension going from one to the other. I think that with Dunlop and Michelin there is a pretty big difference in right height and profile so you need to make substantial changes in set-up if you want to run the slicks.
George
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