The Adaptec 29160 is a 64-bit card (will work in a 32-bit socket as well) but is 33MHz. The Tekram DC-390U3 series supposedly is 66MHz. Adaptec, Mylex, etc., have 64-bit 66MHz SCSI raid cards available. ($$)
Unless you have 3 or more drives talking at once, 66MHz is really going to be irrelevant as the bus at 64-bits, 33MHz can easily handle the traffic.