I think you mistook stamina for endurance. 4000 endurance is maybe a bit overkill.
1.) Sex resist reduces both desire gain and pleasure damage.
first I didn't mistook stamina for endurance (4000 endurance is not overkill, its cheating bcz of the lvl limit, its impossible), but you corrected yourself on the point 2 so np.
second my problem is "sex dmg" mean nothing to me. if reducing sex dmg reduce the STAMINA dmg I take when having sex then I will thake sex resist, if it doesn't I wont bcz it reduce desire gain too.
So I rewrite my question :
Sex resist reduce sex dmg ok, but : it reduce pleasure gain or stamina loss when hit/being hit ? (I know it reduce desire gain now thx btw)
for the creampies point I don't take big stamina dmg from them so its not a problem.
I add another question (but this is meabe bcz of a bug) :
My Karryn is lvl 103 slut lvl add all dick stare passive unloqued but she still insult prisoner loose dick desire when I use dick stare skill. is it normal or I need to rase more my slut lvl ?