This would be exactly my preference. Make 1-10 cover the power level of E6 in 3e and 11-20 the next six or so levels.
I feel a d20 resolution mechanic works most simply and elegantly wth a 10-level system.
Sometimes, in my crazier moments, I envision a D&D-ish game that only goes to level 10, but does it multiple times.
One alternative I prefer is to granulate each of the ten levels, so that being at a level is longer but incrementally more interesting. Rather than having the plateau for each level come but once, at the end/beginning of the level, milestones within the level confer benefits. This is an alternative to a system that stretches the leveling to say 20 or 30 or beyond with benefits coming strictly at each leveling up.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.