Just my personell expericence with the CLS2875H. I use them in two F3A planes and in my opinion they are very stable, centering well, precisious and fast enough and for my flight expericence (i am not a competition pilot) they are accurate enough for pattern flying.
So i can recommend them and would use them in the Viper XL .. absolutely worth thier money in my opinion
Prerequist is that you are using 100% of servo path for full rudder deflection.
One additional word for using the HET 590 in the jetfan with 12S.
I used this motor in my VIPER XL about 3 years ago and was very happy with it ... BUT i tried to have as less weight as possible and reached 7000g flying weight (with 12S 5000 SLS Quantum 30C ,1430g accu weight). With this setup i could fly about 5.30 - 6 min including pattern fly and had enough power for every situation.
One of my colleague had the same plane at the same time using the HET 685 with Jetfan and 12S but hat about 8.3-8.4kg fliying weight due to heavier needed batteries, ...
If every plane flies alone there was no remarkable difference ... everything could be done with my plane as well , same climbing possibility, same flight time, same pattern figures ... ... BUT ... if we flew together i could see that in every moment the plane with the 685 motor was little faster and every pattern figure was a little bigger.
Another colleague had the plane with Jetfan and Leomotion 600 motor at 14S ... and her the difference from the 685 to the Leomotion was more than the difference from the 590 to 685.
Great advantange of my plane was a very easy landing ... but of course no problem with 8.2kg as well.
The 590 motor has a better efficiency than the 685 in that use case.
Hope this helps a little