i've heard a lot of prelude owners complain that their 5th gear grinds. even 5th gens...
well, mine kind of does it too. but one day i figured out how to get rid of it.
then i drove a few other preludes that have the same problem:
-92 Si
-89 Si 4WS
-98 typeSH
-95 VTEC
-94 Si

they all seemed to have the same issue... here is what i discovered:
when you up-shift from 4th to 5th, don't go all the way to the right and then up.
instead, try shifting diagonally without moving your shifter all the way to the right after you take it out of 4th.
it works for me. it also worked on all above cars except the 89 Si.
give it a try, see what happens.

NOTE: i'm not saying this is going to work on your car for sure. i'm not saying this is the answer to all grinds because as we all know synrcos on ludes are not the best.
don't come back flaming me because this didn't take care of the problem.
i did this "research" if you will, because i wanted to see if it's like that for all ludes.
so i drove my friends' ludes, and asked a few other people i didn't even know that well if i could drive theirs to see if they have the same issue.
all i'm saying is that it worked on my prelude and few other preludes as well, so i'm sharing this with you based on my personal results.
hope this takes care of the grind for some of you, i know how frustrating it can be.

 

I would have to agree w/your statement for the following reason.

My 5th gear grind went away after installing my DC short shifter adapter..Which, in turn seem to make all shifts 2-3 4-5 alot more *diagonal*

If that doesn't work, I know a few owners how changed there tranmy fluid to GM syncromesh. I however stuck w/good ole honda MTF.