Pmfranke,
The lower the ratio # the lower your RPM's will be, higher # will be higher RPM's. As for the T5z, the gear howl in 4th and 5th more than likely is coming from your rearend, noices in the rear gear set will travel up your driveline to make you think it is coming from the tranny. As for it grinding going into 5th, I would first check the clearance between your throwout bearing and the fingers on your pressure plate, it should be between .100 and .300. If all is well there and you are getting adequate engagement movement then there is a good chance you have a worn sycro on 5th.
jimig@standardtransmission.com