Comments about Hireko UST65A:UST ProForce 65 Gold:

The original UST PRoforce 65 has been around along time now, and will probably be discontinued sometime soon. I'd get one now while they are still around, and the price just can't be beat for such a fine upgrade shaft.
It gives you a low ball flight with a tight dispersion.
This particular model of shaft seems to play in between true flexes, atlest as it relates to the feeling of a steel shaft (as many graphite shafts have softened their flexes over the past decade or so). The R flex is slightly softer than some R flexes, and softer than a steel counterpart. The S flex seems to play like a shaft that I would consider to be between an R flex and an S flex.
Hireko's DSFI ratings seem to have it pegged pretty well as far as swing speed ranges.
If you have a rapid tempo, I think you could get away with an S flex even at 90 mph, while a slow tempo might be 100 mph.
I'd personally rate the R flex at 80-90 mph, and I've played both the R flex and the S flex.