How much better is 4 minute duration than shorter (.5, 1, 2 min) for VO2 max?

I'm starting the 4x4 protocol, aiming for 85 - 90% MHR, but the way to do that that really works for me (just personal preference) is hiking uphill with a heavy pack. So it takes some time, including getting to the trail I use, and I'm also a little unsure of how it'll be for my knees. I also find that 30 - 60 second sprints on my bike, going all out (and sometimes at the end of zone 2), work pretty well for me. What and how much benefit will I be missing if I do more of those short sprints and less of the 4x4? Thanks for any advice!

p.s. Once a week is all you need, right?