I love Zimmermanns! I do not find the tempos rushed, in fact I don't think they are faster than most of the modern recordings, it is just that they have this springy tight feel about them, which I actually find very appealing. I really like the way they are recorded too - such a full warm sound. Yes, harpsichord on Bach recordings is a bit in the background, but in general harpsichord loses a lot of its timbral colors when recorded with an orchestra (IMHO), and I still have to hear a record where a harpsichord would sound good with a larger group (I love good solo harpsichord, no problems with the instrument in general). And Zimmermanns' Vivaldi is really excellent (definitely not the fastest I've heard and with very audible harpsichord):