But you are still going to make HD highlights right?? What I recommend doing is make your HD highlight like you normally do then convert your finished HD highlight down to SD and upload both versions.
mpeg streamclip is pretty good for downscaling.
here's a some pretty good settings for "SD" or rather what I like to call "mini-HD"
for FPS change according to what your source was.
50 --> 25
60 --> 30
if you are working with an HD that is already normal fps (30 or 25) then leave that field blank, because you don't need to change anything.
another note, mpeg streamclip takes forever to encode avc to avc, probably 3 hours for a 10 min file