For a fair
performance comparison, the $8K more expensive version of the Z4 was used since it was the one most competitive with the S2K in terms of 1/4 mile times and such. Had the comparison involved only price, then the Z4 Base could have be used. However, at that point the S2K pretty much walks away from the Z4 Base in terms of performance. The midlevel Z4 had to be used to compare the performance aspect. When weighing both price and performance (bang for buck) between the two models, you will wind up paying a lot more for a Z4 as to a comparible S2K.
Depending on the price you're willing to pay.
Hope that helps to clear some of the fog.
