a 100hp 750 is possibly a grenade, pre 98 definitely without some serious parts replacement. 900 has the same bottom end (except rods) as a 996 pretty much, so good for 10,000 rpm and 130hp. it depends on how far you are moving from the original design.
later (2001>?) engines have better oiling too, and that makes a long term difference.
944 should be negligible in general use. some high comp, high hp motors (track use esp) with earlier blocks (95 ish) will crack the vertical cylinder stud section out of the cases.
Thanks Brad for a very informative and useful answer to my question!