90 @ 4500rpm isn't all that bad.. I'm turning 4400rpm @ 80mph. If you want taller gears that aren't too tall- you could try the transmission from the 88-91 Civic sedan DX/LX (USDM designations, don't know about B.C.).
Are you topping out because of your rev limiter? I assume that you are. How about rechipping your ECU so you can rev higher? What ECU are you running right now?
If you're willing, you could also crack open your transmission casing and replace the 5th gear with one from a USDM 88-91 Civic... I don't recall the ratios in the ZC transmission off the top of my head (and they're only in my laptop right now), but the USDM 5th is slightly taller.
Just a few ideas...
By the way- I love your setup. I never see anything like that around here. Plus your build is extremely clean in those pictures. Keep up the good work!