Questions regarding Headers: Nautilus or MSDS for an '07

I'm contemplating getting either of these for my '07. Would one be better than the other. The MSDS are a bit less expensive, but are they any better? Lastly, (with price being a factor) would I be able to use the remainder of my stock exhaust setup (from the cat back). My biggest concern is the pre-cat failure(s). I will have to have this installed, as I have niether the time nor place to do this myself. So my thought was to get the headers first, then when the funds are available get the Magnaflow.