I have an old SD set I use for my main dev box and then test on an HD monitor. Occasionally, I'll switch the SD roku to HD, it outputs a squashed verion via the composite, so you could actually get away with testing everything on an SDTV if you had to.
Both my Roku's are the first series Roku HD, so I can't say anything about performance of the newer series, but i haven't gotten any complaints. Some things are different on HD: drawing a full screen image canvas is a bit slower in HD mode, as one might expect given the additional cpu needed to draw to a larger area. The overhang image may need to be adjusted to not interfere with the overhang breadcrumb text. The advertising banner on SD actually touches the bottom of the posterscreen text and doesn't look very good on SD, not much you can do about that but adjust the color on the edges to avoid visual conflict.
- Joel
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