How much difference will it make?

Obviously, you are getting a lot of opinions, but I'll let you know what I do with my Dart that runs 9.90s in the 1/4.

I run SS springs (add a clamp to front segment, remove rear)
I run 4 degrees negative pinion angle
make sure your rear shocks are long enough to let the SS springs do their job
I run Clavert racing 9 way adjustable rear shocks
Cheap summit 90/10s up front.
No sway bars front or rear
275/60/15 MT Street SS (I've never had luck with Nittos)

At your power level you don't need super expensive double adjustable shocks. You don't need caltacs. Don't over think it and don't over spend.

Here is a picture of my car launching on a 9.94 pass last week in Florida at Sickweek when I was trying to go 10.00. Look at the driver's side leaf spring seperation. That's what you want!

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Thanks for telling us that, bad *** dart dude