my hardtail (genesis core) came with 70mm and 680 but i’m currently running 50 and 720 which i like a lot better. i’m 5’6 but was reccomended a 17.5 frame and the more i’ve read the more i think i should have got a 16 (which the lbs didnt have for me to try) my theory is the short stem despite looking slightly wrong makes the cockpit length more similar to the smaller size. it’s certainly made the bike feel a lot more “chuckable”
climbing wise on road it’s made no difference, it is hard to keep the front wheel down on steep off road ascents but i think thats partly my newbie lack of technique/in-experience and i’m not sure i found it any easier with the old stem/ combo