Berg 5 ....I believe your looking at about $2500us in parts alone(someone correct me if I'm wrong) but could be the best of all worlds. ....strong , fits your car(sort of) , close ratios and good hwy gearing.
Bus...strong but very low gearing, not so easy to fit.
Porsche...probably good gearing , cheaper than berg 5 , and even harder to fit than bus ( I think).
Stock ......cheapest , totally fits your car, many upgrades available, but always a compromise in ratio's one way or the other.
just my own sort of a rough over view of the options