Preamp advice - Do I even need one?

Ah right, forgot about that :D And I too am not certain how much of a difference the mic preamp will make, but I would urge you to not give up on the Rectifier until you've at least tried it through a decent interface! (which the Pod is not IMO). And the mic was on the bottom-right speaker (with the cab sitting on a coffee table right at the edge to minimize reflections from the floor), a little under 1" from the grille cloth and pointing directly at the speaker, specifically about 50% on the dustcap/50% off, or maybe even 70 on/30 off - and I experimented with moving it further from the dustcap, but that didn't help the 6k fizz, just took away some of the bite, which I wasn't a fan of!)
 
Also, one thing I've noticed about making impulses - since you're sending the sine wave out to the amp, through the amp/cab/mic, back in to the interface, and then recording it, there's naturally gonna be some latency, and since Voxengo Deconvolver doesn't take this into account, I've noticed that the lower I set the latency on my interface when sending out/recording the sine sweep, the better the impulses sound in the end! Just something to keep in mind :)