I was also going to suggest heading to Upper Krust's site.
I particularly like where he takes the definitions of Heroic, Paragon and Epic Tiers and proposes changing the levels of monsters to actual match those definitions. This is a great starting point for thinking about Epic design because it makes you stop and think, "What is an Epic threat?" I think one of the things that 4E got wrong was making things like swordwings - basically an upper Heroic monster - into an Epic monster despite the fact that it does not pose the sort of threat that Epic should actually be about.
I like the idea of Swordwings for my Forgotten Realms campaign - I just bought 3 Swordwing minis - because in the Realms, "Epic" frankly just doesn't mean that much. Get out of bed and you'll meet 6 Epic Things Before Breakfast, it often seems. That's how Greenwood has always done it - the Epic becomes mundane - and I think that's just how the Realms works. I intend to treat Epic in my FR campaign as pretty much 'high paragon', I think, at least most of the time.
For a different setting I would go with the 'Epic Threat = Destroyer of Worlds' type stuff ok.