sounds like a coincidence to me, plus you were in 5th gear which is "techincally" an overdrive gear (even tho there is no torque converter). what is important here is the final drive ratio
and knowing how honda builds their cars out of legos makes it much more likely that they prob saved thousands of extra blueprints and resources by re-using the same basic final drive design.

the 4th generation si (h23a1) is a non vtec h series engine, which makes less horsepower than your GSR, so ur gsr will spank the 4th gen si
if you are looking for more power get a DOHC VTEC 4th gen (they're rare) or swap an h22a into that si.
that car with an h22a will spank your gsr no prob

~boomer