I dont see how running a spool would slow the car down. I changed from a sure grip to a spool years ago. I dont know the exact weight savings, but I know that my spool is VERY light (just a couple pounds) were as the sure grip unit that I pulled out was quite heavy (30+ pounds) .The weight savings alone are huge, not to mention SOLID, consistent traction on every pass.
Could you please elaborate on why a spool would slow your car?