How did that one go? I actually own the thing but have never played. Did it hold up as entertaining for the entire length? What was the playtime in total?
First, sorry for missing this question for about a month.

The thing with TI3 is that the length of game completely depends on the players at the table and how much your group of people tends towards masochism (complexity) when you get together to play.
If you use the basic game, and keep the imperial card as is, regardless of the other rules you use, you're looking at a 4-5 hour game with 5 players that know what they're doing with the game and move in reasonable amounts of time.
If you've got new people at the table, add a half hour per new person to that time allotment. If you swap out the Imperial card with the one in the Shattered Empire expansion add two hours to that time frame.
The following will cause you the loss of a weekend to TI3.
1. Swap out the Imperial card.
2. Use all optional rules
3. Don't put your most anal retentive person in charge of the victory track and objective cards.
Of the three, the third one has proven in my experience to be the most important. If you have someone who knows what they are doing, watching the victory track, reminding players how to win the game regularly and actively advising of the victory point conditions during other players' turns, the game will go a lot faster.
I've had games go 4 hours, and I've had others go from 1pm to 11pm finishing only when a player folds due to getting ganged up on.