I doubt the different settings would really have that much impact on cpu usage. Maybe a little bit but probably nothing to worry about.
As for other settings, there isn’t really anything else to tweak for this kinda thing. The speed value is quite a traditional thing carried over from older trackers, but I don’t think the speed trick will be necessary in the future when Renoise moves away from this old tick-based method (speed = number of ticks per line). In the future I guess we will just have a much more fine degree of resolution.
You can see in other threads like this one:
https://forum.renoise.com/t/a-question-of-speed/12837
… the speed thing has been in discussion for quite a while now.