Hogue makes grips for 457s that should do the job, just Google "S&W 457 hogue grips" and you should find a bunch. Priced a little over 20 bucks I'd think
8 round magazines for 4506, 4566, etc. will fit but stick out a bit. I think there are 10 round mags from Promag. I always keep my eyes open for OEM S&W mags as they seem to function without issue.
EDIT **Promag webpage lists a 10 round mag with a spacer. Looks OK, fit & function, ??? **
Some quick cell phone pics of my 4516 with the Hogue rubber grip panels. Fit is the same as on my 457. Hope this helps. Can take better pics if needed.
I would say the panels are thicker but not by much. My experience with the grip sleeve was on a 6906 and it was on older grip sleeve. It looks like some of the newer sleeves have a little palm swell to them which the panels dont. Pachymar makes some sleeves too.
I looked at a selection of 4516 grips, and the biggest difference I notice is that it adds a curved swell to the bottom half of the backstrap, so that rather than the stock straight profile they give the pistol a curved profile.