You haven't given us any information on your video file / size / format / etc. 10 Bit what? Uncompressed SD? Is it interlaced?
You can't export higher quality stills than they already are in video form. In other words, a DV still exported as a TIFF will still look like a DV Still...just will be a larger size. IMHO, a good option is to export a "Still Image / Tiff" from a single frame in FCP.
When life gives you dilemmas...make dilemmanade.