Instead of putting in an entire new set of gears, why dont you just reduce your wheels size, and get the same effect for a lot cheaper?

Plus you could also change the driving back to stock, simply by putting the stock wheels back on.

I imagine some 16s or even 17s with low profile tires would do the same trick as the gears. It might look strange at first, I mean we are used to seeing 19s in the back, but some 17s couldn't look THAT out of place. You'd have a little bit more wheel gap but 17s are big enough to not look like you have a lowrider. However you'd get a lower center of gravity for cornering, versus stock wheels, and the faster accelleration that comes with reducing wheel size. This car would fly with 17s in the back, those 19s look good but have to slow it down a bunch. 16s would just be ridiculous but I think thats more what your going for.

Ok heres another idea, coilovers. If you go with 16s or 17s, you can drop it at the track with coilovers. Then you get the accelleration you want, super sharp handling since the car will be so low, and no ugly wheel gap. Then when you wanna go back to stock, raise the car back up and put the stock wheels back on.