3kramd5 - I shoot JPEG with the various adjustments and RAW in the hope that I've got something to work with if I cock up. Also, as you are probably aware, the SD card slot is crippled and it's faster to save JPEGs to SD.
Yah, I know. It's not crippled, it just pre-dated faster SD. I personally haven't run into buffer issues (I shoot RAW to both cards), but I don't burst often, so perhaps that's why.
Personally, I do a lot of things out of ease, so with that in mind:
Once you're out of the field, if you haven't have a failure in the CF card, do you keep the JPEGs?
If so... why?
If not, then just keep them on the SD card as you delete from CF. They're small enough relative to RAW that you aren't likely to fill a card with them with the balance of space freed by deleting RAWs, right? How big is the best quality JPEG relative to RAW? Let's assume they are 66% as big. Suppose you can fit 99 JPEGs or 66 RAWs. You'd have to delete and re-shoot literally 1/2 of your RAW files (that is, shoot 66, delete 33, and shoot 33 more) before filling the card with JPEGs. And even if you would fill a card, just get an extra SD; it's cheap, and then you never have to think about synchronizing your deletions. Just replace the SD when it gets close to capacity so you don't fill it at an inopportune moment
It is a little weird that canon basically handcuffs us when it comes to accessing files on the secondary card. Sure, you can change the playback setting, but that's a PITA. But while weird, it's never been problematic to me.