i'm using a steeda tri-ax on my car with the t5, works well, you have 2 options on height, im using the tallest option, works well for me.
some people don't like the triax because it has a notchy feel to it.. but for aftermarket shifters, here are your choices that I know of.
Steeda Tri-Ax, Pro 5.0, Hurst, B&M
There may be more, but those are theones I know off hand. It seems to be a personal preference between all of them, I like my Tri-Ax, my dad doesn't, he wants a hurst. I've heard negative from a few people about the Pro 5.0, as well.
I would say go with a short throw though, T5 + short throw, vs my rad 4, felt like I had a foot less of travel between gears.
i was thinking of going to an after market shifter but depending on the money i might go with the one that is offset so it puts it back in the mustang II stock location. i have an email into the company to see if they are still making them. they were making them for a t-5 swap into a merkur xr4ti.