You first need to find out what overdrive ratio your T5 has and then pick a rear gear to match. T5's range in OD ratios from 0.18 to 0.33 (or 0.82 to 0.67). A non world class T5 is a very weak transmission so if that is what you have I'd forget tire smokin. World class ones are stronger but still a wimp transmission as far as tolerating high torque. It is much easier to find w/c ones from Mustangs and they usually have the 33% OD. If you have a 4.57 rear and a 33% OD T5 then your final gearing with in overdrive would be 3.06 which is a very good road gear. An 18% OD T5 would give a 3.75 final---not so good.
Lot's of good advice there. I would have to agree. Before thinking about rearends, lets see what Trans. you got then go from there. Better yet, install it and see how you like it. There were almost 300 variations of the T5, so trying to say which one is good, which one is bad is nearly impossible. Truth be told, your rearend is about as strong as it gets, no need to swap it out unless you have to. Not to mention the 14 bolt is a big heavy brute. You'll probably lose some horsepower just trying to turn it's enormous brake drums.
The Mustang and F-body (Camaro) guys have been beating on the T5 for years. There's plenty of aftermarket parts and upgrades for it if you so choose. The 235 or 261 aren't really known for their abundance of horsepower or torque for that matter. I would think just about any T5 would hold up just fine.
Here's some good reading for you.
http://www.britishv8.org/articles/borg-warner-t5-id-tags.htmhttp://www.fordmuscle.com/archives/2005/12/T5Rebuild/index.phphttps://www.astroperformance.com/product/cluster-support-plate/
