As far as normal driveability goes it will be fine, but if you plan on getting into the boost pretty heavy, that's where it will take it's toll. It may even be noticed when trying to merge getting on the freeway when on a short entry ramp where you need the boost. If you run the proper octane and play with the boost, then drop the octane and do the same you should notice a drop in it's performance, but with average driving you will be fine on regular. I wouldn't try running against someone unless they are no competition to begin with on regular. Besides, premium is just all around better for your SRT-4 anyway. I myself run no less than 94 octane with occassional use of 100 octane when the gas prices get high enough.