I think I finally found the sweet spot for my 17.5 SP Ultrasportsman on the SPX. With a SMC lipo, I'm running a 4.07 FDR on profile seven and it comes off the track in six minutes at about 155 F in ~90 F ambient temps. I've found that any small deviation in profile or gearing makes the motor feel quite weak or overheat. The brakes have always been excellent with this speed control and motor combo. I've already ordered a Novak 17.5 though, and I guess I have to do a comparison.
I use the same electronics for my 13.5 car, except the motor of course, which is a Novak 13.5SS. The FDR I am using is 6.1 on profile seven and the motor temps about the same as my SP 17.5 after six minutes. I'm going to try gearing a tooth down soon; that should be about perfect for our track as I may need a slight bit more punch coming off the last corner and going into the straight. The brakes on the Novak aren't as good as the SP, but overall I feel that it is a better motor that isn't so finicky with FDR, power profile, and temps.
I have no regrets about going with the SPX and I've been recommending this speed control because of it's performance, cost, and ease of use. The other "new generation" speedos are great too, but I don't think that the SPX should be counted out just because of a lack of software updates. For me, the SPX has proven to me its worthiness in a field with KOs and Tekins.