If you're happy with 2 superflashes, then I suspect two MiNewt 600's would be overkill.

On the other hand, I just got a MiNewt 600 last week, so I'm still in the "wow, that's bright" phase and haven't yet settled into the "I could use more light" phase. The first time I hit that level, I may be able to just start using it on high.

My experience in one week is this: If I'm on a well-lit road (lots of street lights), any of the 600's modes is overkill and does little more than add highlights to what's already visible. If I'm on a marginally lit road (some street lights), any of the 600's modes is sufficient and does a good job of lighting the road surface but has little effect on peripheral objects which are already visible from the street lights. If I'm on a poorly lit road with no traffic, any of the 600's modes is sufficient and does a good job of lighting the road surface and revealing peripheral objects. If I'm on a poorly lit road with oncoming traffic, the medium and high modes do a decent job of lighting the road surface and overcome the pupil dilation effect of the oncoming headlights.

In my garage with the lights out, it's easy to see the dramatic difference between medium and high. On the road, it's harder to see the difference.