The larger cuttings (10-12") do seem to root quicker, but you should do fine with 3-5" cuttings if you want to maximize the cane you have. I had a student do a science fair project that involved propagating Miss Andrea (the Miss Andrea, which was my first cordyline, came from cuttings from my garden) and evaluating what product would help produce the quickest roots and top growth. He used rooting hormone, Super Thrive, Ferti-Lome Blooming and Rooting Plant Food, and one other product besides his control group. The cuttings were about 4 inches each and all rooted and produced leaves (and all 20-30 cuttings are still alive and well), but I was very surprised to find that the Super Thrive cuttings rooted and sprouted quickest (the Super Thrive was only applied once in the water when the cuttings were first potted up). I had assumed either the rooting hormone or the Ferti-Lome would get them rooted quickest. I thought it was a great project, but the judges at the Regional Science Fair were not as impressed. May have another student try something similar next year with a different cultivar.
I gave a cutting of my Earthquake cordyline to another grower, and it was only 3 inches at the most. It currently is bigger and healthier, after being grown inside a greenhouse for a couple of months, than the original that I put in the ground at least 6 months ago. The constant water and fertilizer really pushed it along. I really don't have any space to keep them potted, so once they root I stick them in the ground and they usually do fine. The last batch I just rooted in water with some Super Thrive and the Ferti-Lome added and they sprouted/rooted quicker than when I used to pot them up and let them grow out in the pots with regular water and fertilizer before being put in the ground. They would probably do better in pots with bottom heat, but I can't be bothered when you can just stick them in the ground and watch them take off.
You obviously have far more experience than I do, so your judgment will guide you through the process. Good luck. I hope you have great success with the Pink Floyd cuttings.