I am replacing the front sight on my 629-4 and trying to come up with the optimal height (for me). I would like to use the lowest front sight practical for both holster fit and aesthetics.

In general, heavier bullets shoot higher. Do bullets of the same weight generally impact at the same height regardless of velocity (within reason)? For example, generally would there be a significant impact shift between 240gr bullets at 1000 fps and the same bullet at 1200 fps, and if so, do the faster bullets impact higher do to greater recoil or does the fast barrel time offset this and cause impact to be lower?

Thank you.

Slower bullets of the same weight will generally shoot higher due to dwell time.

Momentum is the major factor. Loads with the same momentum, even though they differ in velocity, will impact the same elevation.
Greater the momentum, higher the impact point.