Quoting 4thStroke:
As far as the roll bars go, I've never experienced larger roll bars having an adverse affect. If it improved handling characteristics, it was worth it. In my case, it helped.
Bigger roll bars will help to correct the extra roll that's induced when you lower the car and shift the roll centre - they can even give less roll than stock, the car may feel better, it'll probably be faster than before too, but it'll be faster still if you pay attention to getting the geometry right.
Read this:
link How to make your car handle - racing chassis racecar engineering .pdf
and this:
link Tune to win, by Caroll Smith .pdf
It's similar to how you can roughly tune a car with an s-afc, sufficiently to make some power and not blow it up - but something that gives better control of fuel and ignition timing will allow you to get the tune closer to ideal, and thus make more power.
If you want to compete, near enough isn't really good enough.