I start leaking right after switching to vavoline synthetic. I ended up having to buy a high pressure hose. Major PITA. I went back to normal atf-like the manual calls for(for my mk3 anyways)-and just plan on changing it every 30,000 miles or so. How does one PS fluid outpreform another? It's just a hydrolic(sp?) fluid. You cannot really compare to changing old 60,000 mile fluid to new synthetic stuff. Has anyone tried changing them out in like a week or something? I don't personally think you'll notice a difference between reg. atf and synthetic as long as it's new fluid. Just my opinion.
In the past people have been concerned about switching from regular oils to synthetics in engine oil after time because synthetic oils do not "swell" seals and O Rings as much therefore leaks may develope. In reality in most any engine (especially turbocharged ones) the benefits of the synthetic outweigh the potential cons.
However on a Power Steering system which has lots of little seals and O Rings, this may cause problems. I have not heard anthing certain along these lines, but just drawing a conclusion from what I know about synthetic motor oils.
That being said, in a PS system, I don't think its worth $11+ a quart to use redline ATF in your PS if you don't have to. Plus using Redline ATF in a Supra tranny is a surefire way to make the road to a SP tranny much shorter.