Personally I'd say the 4.5" is too small. Even a wee hamster should be able to move a bigger wheel. My little robo has to climb into his wheel (I make the substrate a bit higher at the front or put a couple of flat wood chews that he ignores in front like a step). I think the problem is with the silent spinner, not your ham. They redesigned them a while ago and now they don't spin very well so all hams are having a hard time moving them. Pets at home do their own version now and it's nearly the same. The plastic stand is pants though so I'd put it on the metal silent spinner stand for safety but get the same size you have now.
I made a little video comparing the p@h version with the original superset/kaytee silent spinner. The spinner in my video is over a year old & from before the redesign and has none of the stiffness of the new ones. The p@h wheel I got just before Christmas.
Hector demonstrates....silent spinners - YouTube