Tranny first gear combined with rear gear help

hey guys thanks for the advice,

first off my tranny is a world class, its the higher rater one besides the z spec rated at 300ft/lbs...its from a 90 mustang and its made by borg warner, not ford...a new clutch kit will definatly be in the works for it...my car wont have 500hp right now so when it goes it goes, but i dont expect it to happen soon...when it does i plan on upgrading with the g force stuff or something more econmical from astro performance...my car has a snubber, will have stiffer springs, and it will have subframe connectors as well...what do you mean when you say granny gear? is that good or bad thing? sometimes i wonder if i should go with a 4.56 gear now, as i could still cruise at around 2500 with 28 inch tall tire i plan on running