Getting the SD torrent will be a bit faster, indeed. Less to download, less to process.
The quality will be less than what DVD video is capable of though. If you want to watch it on a big TV you may want to get the best you can have on DVD.
The SD release is 624x352 or something in that ballpark. You're trying to squeeze that into 720x480 (assuming NTSC based on your location), meaning you'll scale up both the width and height. Even with today's smart resampling algorithms there will be imperfections. With the SA special there may also be increased xvid compression issues because it's 75min instead of the usual 60min while still at 700MB... you won't notice them on regular screens, no idea how large your TV is.
If on the other hand you use the 720p one you'll downscale from 1280x720, so every DVD pixel will get unique info. 75min onto a DVD5 will give you boatloads of bits per pixel preserving as much as possible of the HD goodness, while of course at the lower DVD resolution.