I have to agree with Harm that unless you need to mix the SD footage into an HD project for some reason, best to stick with SD. When done right, SD footage on DVD can look very good on an HD TV, when using a DVD player or Blu-ray player that upconverts to HD and connects via HDMI. Take that same SD footage into a Premiere HD project and burn to Blu-ray and it does not look so good at all.
Also, SD footage is typically not 1.33 anamorphic, and SpeedGrade is for color grading and has nothing to do with standards conversions.
If you can tell us the workflow/purpose of this adventure, we may be able to offer more specific guidance
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