Just to be the devil's advocate, here - why NOT buy 20s? I mean, realistically, how many of us are going to be able to extract that extra few percent points of performance ON THE STREET, when using 19s in lieu of 20s? C'mon, be reasonable. To be able to appreciate that extra performance on the street, is every so slightly irresponsible, to say the least.
I bought HRE 20s for that exact reason. I like the looks, and for the street, they still offer as much performance as I feel I should/could deal with (I reiterate, on the street).
That said, I also have a set of OEM 18s for the track, and also have a set of OEM 19s just in case I decide to go with a BBK.
Gotta cover all bases, LOL.