Stick with your tranny. If you want shorter gears, go with a GSR.
Which TD05 turbo is it? There is a 14b, 16g, small 16g, 18g, 20g, etc....
Any of those turbos are larger (in flow capacity) then the t3. The t3 you have (which is off the older 300zx's)is a 60 trim. The same turbo I have on my Z. They're good to around 280whp give or take. The mitsu's are good for 300+.

I generally don't suggest mitsu turbos on Hondas, mostly from personal preference. Although I have a friend making 260ish on 10psi from an 18g.