I did the SVT brake swap back in 2004. I also did stainless lines with mine at the same time.
1.) No need for a proportioning valve, they work just fine
2.) 20-30% better braking than stock, nice improvement over stock for not a fortune, plus you can still fit 16" rims for winter tires on the car ( I do).
Speed is only a matter of money; how fast do you want to go?