Mixing SD and HD footage in the same timeline

I've read a few posts on this topic, but some of them were relatively old. So I thought I would refresh the topic.

I'm using Adobe CS5.5. What is the best way to combine SD DV and HD 1920x1080 footage on the same project/timeline? And I suppose the answer depends on if I'm burning to DVD or Blu-ray? Well, how about both:

For DVD...
-Should I scale the HD footage down in Premiere? If so, should I still use 'Maximum Render Quality' in Encore?
-Or should I scale the SD footage up on an HD timeline and let Encore convert everything back down to SD?

For Blu-ray...
-I suppose the only option is to scale the SD footage up and use 1920x1080 timelines all the way.
-Are the upscale converters (Red Giant, Boris) worth it? Preference?

And if it's not too much to ask...what are your preferred transcode settings in Encore for Blu-ray discs? This is my first dive into HD and I want to make sure I get the best quality possible.

Thanks for all the help.
Bruno71