Running twin 750HP (Whipple 525s) on XRs with Bob Machine Nose Cones / Drive Showers. They’ve held up great pretty good over the years as boat is driven with caution no wholeshotting etc. Wanted to know if putting a Imco lower will strengthen the drive at all or will it not do anything more since the upper is the weakest point? Also considered drive guardians but as I don’t do any wake jumping; was told I wouldn’t get much benefit from them (Lake boat rarely rough)

The lower will do nothing strength wise, I would putSCX uppers on it at the minimum
for an upgrade

I second SCX upper. With your power and boating in what sounds like a calm lake, I don't think you need the SCX lower or Drive Guardians.

I have whippled 525s. My original xr’s didn’t last one complete season. Changed to SCX uppers with sc lowers. Have had five trouble free seasons. As has been stated a lot of things can affect durability but it’s generally a good combo to work with.

SCXs. More time on the Water. Less time pissed off because you wasted another XR.