David - I presume then that you run a truck mount as your no1 extractor?
All the big hitting pre sprays are much of a muchness when running a porty, it may come down to the label you like the look of most! Some love the stuff that others hate.
your using formula 90, and it works for you ,so stick with it, I know its not classed as a pre spray but many on here use it that way! and it works for them also.
Power burst, Champion, formula 90, Ultimate Master are all great products! -and there's loads more!