[SpEEdyBL]

I have the Neu-Castle 2650 (like a 1512 1Y) and a Tekin T8 1900 4030 (like a 1512 1.5Y). The 1900 on 6s is much faster and has much more pop than the 2650 on 4s, both geared 14/46. The 1900 also runs about 15 degrees cooler. I'd say the the 1900 on 5s geared 16/46 is still a little bit more than the 2650 geared 14/46 on 4s and runs 25 degrees cooler. So you may notice a considerable difference if you go with 1515 1.5Y on 9s vs. a 1515 1Y on 6s.