Hmmm. It's a tough one because it's always going to be a trade off between quality and file size.
A lossless format (great for archiving purposes) will produce massive file sizes but the opposite is true for a lossy format (but with a potentially great choice of intermediate codecs that are suitable for editing with. They are usually proprietory and so have to be paid for, but man the quality can be off the charts good).
If it's a question of quality with a reasonable filesize, then ideally you'd use (may God forgive me) Apple's ProRes (a pretty much universally accepted intermediate but proprietory codec) or one of Avid's DNx codecs (if you've got a licence) since these can give very good quality images with fairly acceptable file sizes, but I don't know if rendering out to one of those is possible with SpeedEDIT.
Since you're using Premiere Pro CC, I guess I'd render the RTV's out as image sequences and load them into Adobe Media Encoder, then export them as a DNxHR/DNxHD codec or maybe one the the higher quality h.264 presets available. That would pretty much guarantee as near to the original RTV version as possible.
AVI Uncompressed would be the most obvious choice but man, those file sizes really make them only suitable for archiving purposes in my opinion. Then there's the possibility of compatibility issues between editors.
Either way, whatever you end up rendering out to from SE, I'd run the resulting file through Media Encoder to get an intermediate (or proxy) I could edit with.