Here is my experience with this. This will be fairly long and detailed.
Due to an irrational obsession with weight, I crammed my foot into a skate that was too small. While the boot wasn't terribly uncomfortable, it was easily 1/2 size too small, and maybe even close to a size.
These skates were the first incarnation of the Jetspeed which were always bigger than the size by a half, and maybe even a little more. If you wore a 7 in today's skates, Bauer or CCM, you could buy a 6.5 with no fit issue. I don't know if the other CCM skates had this characteristic, but the Jetspeed from 2015 did.
i bought these skates October 2017. My LHS had them in the back. Top of the line Jetspeed, 300 bucks. It was a junior size 5.5. I wear a size 9 dress shoe. I bought them, and the boot fit didn't bother me, especially once I got on the ice...but, the second I got on the ice with them, everything else felt completely squirrelly. I felt unbalanced, I felt like I wasn't going anywhere, I felt weird on pivots, couldn't Mohawk.
I took them in and my guy said the left blade was bent. He put in new hyperglide, but that was still bending. He figured out the holder was mounted poorly, so he undid a couple rivets, pushed the holder in to place and locked it down. He didn't drill new holes, he just made that adjustment. He then put the blade in the straightener and straighten it out pretty well. No improvement in balance or stability.
Then it was suggested that I go from the stock 10 foot neutral to a 11 foot +1. It seemed a little better, but wasn't nearly what I wanted. I still felt awkward and unstable. I got CCM to give me a second set of holders and hyperglide through warranty. I didn't put the holders on, but had the steel profiled to 13 foot +1. It wasn't an improvement. I lost some glide, it felt grabby, and it didn't improve my balance problem in the least.
Then I tried something else. I wore my old skates. Jetspeeds, same vintage, but bigger size. The boot was longer and roomier, the holder was bigger, the runner was 263 instead of 255. It made all the difference. These skates were shot, but I got the message.
I went to LHS with my year old size 5.5 Jetspeeds, and traded them in for better fitting skates with the 263. They are the newest version of the Jetspeed Xtra Pro Plus SMU. With the bigger boot, longer holder/runner, my balance issue disappeared. The stock 10 foot radius and neutral pitch was better than all the profiling work I had done to those junior skates I tried to use.
Each skate is 100 grams heavier. I don't feel it, because everything else is better. Everything. I am balanced, fast/quick footed, and much more efficient. Sure all things being equal, I would gravitate towards a lighter skate, but not at the expense of everything else, which is what happened with me. Weight should never be a priority. I learned a great deal here. I learned my lesson.
I will always experiment and try to make improvements in my equipment, but I wanted to share this with people who might be experiencing a similar lever of frustration. Please let me know if you have questions. Sorry about the book length post, but hopefully it will help someone out.