what flex does the high five come with?
id say try it and then see if you want it stiffer/softer, no use in spending money when you may actually like the tongue it comes with.
4 might be okay, i dont know how you ski or what equivalent flex you were riding before, but i have personally had occasions where my boots flexed way more than i feel like they should have haha.
give the stock tongues a try and go from there