Hi mario14957,
I agree that M3/M4 coding is easier, but it may be because that was the first serious MCU I moved to from PIC micro back in 2009 and I have pretty much used all the features/peripherals of ST's M3s over the years in different applications.
Although I use ST's M3/M4, I think NXP offer much higher clocked cores that you may want to have a look at.
The M4 has a built in FPU in the CPU much like the F28069 I assume. I will try to do a benchmark comparison of FP ops on F28035(CLA), M3 and M4 when I get the time. (I don't have a F28069 so can't compare that)
Regards.