The large is a pretty big bike for someone under 6ft. The reach and ETT on the medium are more like what most bikes would have had on a Large in 2014 and XL in 2012.
The wheelbase on the large is pretty big too.
I’m 5’11, and on a medium Giant Reign, which is almost identical to the medium Strive race. I could fit on a Large with a 35mm stem, but it’d be too much of a handful in tight corners. If I were riding big open DH trails all day long, then it’d be ideal. But I’m not.
You’ll *fit* on both, you may not be able to run a 150mm dropper on the large, but someone with a large and your height will need to confirm.
I’d base the choice on what type of trails you’re riding. Tight, twisty trails – medium, long, straight, max speed DH trails and uplifts, large.
You can use a 50mm stem on the medium and a 35mm stem on the large to get pretty similar reach and ETT. You’ll just have a more agile or more stable bike.