The older TA45's were a 63mm compressor wheel (if memory serves me correctly) which would be the same as the TE63 as sold by Precision. The new TA45a's are a 66mm compressor wheel. Big difference in power!
To fully utilize the potential of this turbo you will need 55lb injectors at the bare minimum. You might even want to go 72's.
You will also need ported heads, cam, etc. This is a solid 10 second turbo, but you will be running 25+ lbs of boost to achieve that. You will also need a 3500+ stall convertor.
Some of the guys I have spoken too recommend the .82 turbine housing as well since it seems to be good for another 2-3 mph in the quarter.
I have a TA45a on my own car and love it, but you do need a lot of supporting hardware to go with it.
The reason why many go with the TE44 or TA49 is that they seem to work great with stock heads, cams, convertors and more modestly sized injectors. To get 125 mph+ trap speeds as you mentioned in a previous thread, you will be spending some loot. Besides the fact that at that ET level with the 25+ pounds of boost, you will want to girdle/cap the short block as well as several other mod's if you dont want to scatter it all over the pavement.
Another option would be a TE70 as you can run atleast the same ET's/mph at lower boost levels, but you will also need more convertor. Geno went 9.90's with his 70. I know Reddshotair loves his 70 as well. Maybe some of them will chime in.