The reloading manuals might say that, but in my experience, of the 13 .22-250 rifles I've shot/loaded for over the past decade every single one was able to adequately stabilize bullets as heavy as 64 grains without appreciable degradation of terminal performance.
Aside from the Savage, all the others had the slower twist. Over 65 grains and groups started to really open up in the latter rifles, with several showing clear signs of instability and eventually several keyholes.
In practical terms, centrefire .22s are legal to use on caribou in Labrador. Local Innu and Inuit are very fond of the .22-250 and have used it extensively on caribou, seals, black bears, wolves, moose and even polar bear. If they can find it, factory 64 grain Winchester Power Point ammo is very popular and I have seen multiple one shot kills on large stag caribou that were almost certainly larger than the average eastern whitetail in N.B..
I'd still prefer to stick with my .308 Win or .30-06, especially if an ice bear might be in the mix, however remote the chance, but the .22-250 can reliably take caribou sized big game. As such, whitetail shouldn't be a problem if you do your part.
Is it the ideal choice? Obviously not, but with good ammo, reasonable distances and a hunter who has put in the trigger time to hone his shooting skills to where he can place his bullet in the kill zone with complete confidence the risk of a sub-optimal outcome is minimized.
As a handloader, I was able to try a number of different premium bullets. Of these, the two standouts were the 60 grain Nosler Partition and 53 grain Barnes TSX in the slower twist barrels.