pros and cons rack vs. original KiPro

We have on order the original KiPro but we can change our minds. It is going in a flypack with a panasonic mixer. We will be editing in Avid MC 6, FCP X, and legacy FCP 7. Is it worth changing the order and the extra $265 for an extra 250 drive which comes with the KiPro for the rack version? Is recording in AVID DNxHD codec a big improvement over Apple pro res when working in MC. I'm just learning AVID (an ex-FCP 7 user). (the codec question I did also ask on the AVID forum). I need to let the vendor know very soon.

MacPro4,1 2.66GHz 8 core 12gigs of ram. GPU: Nvidia Geoforce GT120 with Vram 512. OS X 10.6.x; Camcorders: Panasonic AG-HPX170, Sony Z7U, Canon HV30/40, Sony vx2000/PD170; FCP 6 certified; write professionally for a variety of media; teach video production in L.A.