Will it work ok with my Varistream?
It certainly will
Will the pressure still be the same out of the jets?
No. You'll have to recalibrate the Varistream, but that's quite easy. I can't find my bookmark on how to do it, but contact Williamson Pumps - they'll tell you or give you the link.
Ideally you need a pressure guage on the hose and keep turning up the inside dial till you get the pressure you need in the new hose with the end shut off. The easy way is to keep turning the dial till the spray from the jets "feels right"