Well, accommodating "high-level play" was one of the explicit design principles we followed in Legends of Anglerre, and IMHO it does it well. I'm a long-term Glorantha fan, and wanted to be able to play heroes and demigods in a cool and crunchy way, plus one of our writing team was a huge fan of Exalted and wanted to achieve similar effects. We wanted Legends of Anglerre to accommodate a very wide range of power levels, from gritty 1st level stuff, right up to gods, demigods, and heroes.
So, scaling through the various "power levels" is built closely into the system. Many games use only one "axis of power", ie you start at 1st level and you keep getting awesome in the same direction till you get to 20th or 30th level or whatever; in Legends of Anglerre, we use several "power axes" to gauge character power level, as follows:
i.) Skills
This is actually the least effective power axis - you can use your advancements to improve your skill pyramid, right from Good (+3) up to Legendary (+8) and beyond. But, as you hit higher levels, the number of skills increases and the pace of advancement slows - that's a feature of the FATE system - and so, as a "high-power" mechanism it becomes proportionally less important as you advance. You don't necessarily need a high skill level to be totally awesome.
ii.) Stunts
A lot of the power differentiation between characters happens here. Because stunts can have prerequisites and be "chained" together, characters can become very powerful in *key areas* by selecting stunts appropriately - and the more stunts you have, the more powerful you are in aggregate. A character with 5 strategically-chosen stunts will be pretty awesome in one area; with 10, you'll be very awesome in 1 area or pretty awesome in 2; with 15, you'll probably have unlocked some very high-powered stunts indeed, and may well be a campaign champion in your chosen area.
iii.) Occupations
This is the "focus" of character power-level advancement. You can chain occupations together - use occupation stunts from one occupation to "unlock" access to another, and so on. So, you can move from "Holy Warrior" to "Divine Champion" and then to "Demigod" - each of these being major campaign changes, and allows clear movement from one occupation "power level" to another.
iv.) Spin
We tweaked the FATE spin rules to allow for extremely high effect numbers - partly a feature of using d6-d6, partly of high-powered characters with high-powered stunts. So, for example, some stunts let you generate multiple points of spin *in your attack roll* (ie not just on defence), and then use these points of spin for awesome effects - such as taking out multiple minion groups in one swipe, attacking out of scale monsters, making area effect attacks, and so on. The Combo rules likewise are another way of generating some awesomely high-power cinematic effects.
v.) "Non-character" Power
As characters get more powerful, they can start investing their power in other things, such as baronies, kingdoms, and even starting their own religions. These are very effective extensions to a character's power; someone who can command the loyalty of 10,000 worshippers is a force to be reckoned with.
vi.) Style
Many games treat "power levels" as a continuum - ie you naturally get better at killing bigger and badder monsters, and that equates to your power level. Legends of Anglerre provides for another axis - that of "style". In other words, when you move to an "epic" or "mythic" style of play, it's not necessarily your absolute power level that "increases", but rather that the themes and nature of the game changes. I don't think anyone would doubt that Frodo Baggins' adventure was anything less than epic, verging on the mythic; but he didn't have to be a 30th level badass monster cruncher to get there. That's what we wanted to handle.
All this taken together gives you a game where "power progression" is built into the whole system, allowing you a lot of fine-tuning and some very high-power effects.
Cheers,
Sarah