I have been playing normal speed on duel maps with 6 AI opponents.
This may sound weird, but it rocks!
I love CIV, but normally the game just takes way, way too long to play.
On the duel size map I can finish a whole game in a weekend. I think the smaller game is just great. Fewer cities and fewer units means more tough decisions. Each choice made matters more because it has a relatively larger impact on the empire as a whole. And, when I finally get to modern warfare late in the game I am not totally burned out by having to move two hundred units each turn.
There are three main detractions from gameplay to this setting:
1) Map exploration is over before you can get a second scout built.
2) Barbarians never appear (there's quickly no unclaimed space left.)
3) The (relative) cost of building Wonders become huge.
When your army is 20-30 units 300 hammers for a Wonder is no big deal. When your whole army is 8 units, 300 hammers is a major commitment.
But, I sort of like #3. It's part of the whole idea that with smaller maps each decision you make has a relatively bigger impact.
All in all, losing the early barbarians is a more than even trade off for actually being able to finish some modern wars.