Yeah, the RSD upgrade is very similar to the '14 in that regard. He just came out with the second revision of the upgrade which added a bit of rear bite. I went ahead and just took a deal on the v1 because I wanted the extra bit of steering and always felt like I never lacked for rear traction on the T4.
It was a night and day better car. I still have some playing to do with it (mostly just putting down more practice laps) but I finally feel like I can drive the car aggresively in 17.5 blinky.
Just as a comparison, I went .2 faster on the hot lap with the RSD upgrade than I did on the stock T4, and this was on a really dirty and dusty track.