i have both apples and pears (and a number of other things) with grafts i’ve done as high as 6 feet. no real problems to speak of.
a high graft, especially early on, before there’s enough growth up above to give the lower trunk some shade, might encourage more attempted lateral growth from the rootstock, but new grafts need a little upkeep anyway. i might have more reservations if it was a really dwarfing rootstock, but a semi-standard like m-111 that’s known to be pretty vigorous, i wouldn’t worry about at all.