I've used Vegas & DVD Architect with my HDR-HC1 a bit, so I'll share my experience with you. I wish they would have done a formal review of this combination too!
I also have Pinnalce 10.5 and agree with most of their comments - it's awkward and expensive to license all of the different features and activate those licenses. While the entry price may be cheap, I'll bet it costs as much as the more expensive packages once you've bought the add-ons. In addition, I've found Pinnacle to be extremely sensitive - installation and stability problems abound if you install many other apps on the same box. For these reasons I've given up on Pinnacle.
Editing in Premiere and Pinnacle is very slow with HD files - they're gigantic. A one hour tape is about 11gb on your hard drive. Scrubbing through the tape can be rather monotonous if your box isn't cutting-edge, as mine is not.
But I must say, Vegas handles it beautifully even on my box. You can scrub right through the video as if it was DV quality. I'm running a 3ghz Pentium with 1gb of RAM. I do have fast RAID-0 drives which helps a lot. Vegas is very powerful, and pretty easy to use.
Dvd Architect is ok. It will read chapter points set in Vegas, which is nice. It really does take quite a while to encode the video to create a dvd. If I recall correctly, about 6 hours to encode a one-hour HD tape down to DVD size. But the DVD was beautiful. There are lots of features in DvdArch, including many advanced features. But one basic that I haven't been able to figure out: If you have a menu with several clips on it, after you click on one, I want it to play from there to the end without going back to the menu at the end of each clip.
If you're happy with the videos you downloaded, I'm confident you'll be ok with Vegas as long as your box isn't too underpowered.