Borg Warner makes really good turbos that are proven. There's a reason they are used in a lot of factory turbo applications. Same goes for Garrett. Precision makes great turbos as well. You can get Borg Warner turbos though for cheaper than an equivalent Precision or Turbonetics unit and outperform it. The S475 and S480 turbos are tried and true for 800+hp and 1000+hp applications. If it was me... I'd run twin Holset HX40s.
Borg Warner turbos have lived in diesel trucks for hundreds of thousands of miles and done so for decades. Their reliability is definitely proven. The same goes for Holset turbos.
So long as you have the right converter and gear, the difference between the .81a/r and .96a/r won't be noticeable as far spool goes. The .96a/r will make more power though. With the right cams and converter, spool response when you punch it on the highway will be almost identical.