Maybe you should try to decrease the tremor, rather than try to find the "best" IBIS. Do you drink coffee? If so, change to decaffeinated. Same for soft drinks. Dark chocolate is a surprising source of caffeine. Medications can also help. Have you tried any (usually beta blockers)?
With regard to IBIS, I can only echo what I hear from camera reviews and I only listen to reviews of Nikon, Sony, and Canon camera: Nikon is best, Sony is close, and Canon is not so good. However, recent reviews of the recently released Canon R5 II suggest that it is much better than previous Canon models.
I have a Nikon Z9 and am able to get sharp images at 600mm and 1/100 second hand held with regularity.