Suntour has no shift issuse between 7 and 8 as they maintained the same spacing from 7 to 8 speed cassettes. So switching over makes no odds.
Weirdly this also means the spacing is really really not that far from 8 speed shimano when totalled up....well closer than 7. So 8 suntour runs dandy on 8 sp shimano cassettes (ive done it for 30 odd years).