I would say it depends on what the CD is for. Is it the final product, or is it more like proofs they can look at and then order what they want in the size they want? If they're proofs, leave them as is. If it's a final product, you'd have to find out what they want for 4x6's (or any other size that's 2:3 aspect ratio) and what they want in 8x10 (1:1.25 aspect ratio),and possibly any other aspect ratio (like 5x7), and you'll have to crop those beforehand.