[Khabbi]

The tourneys I run are always 10-12 player T1000 tourneys. We use the same structure as you do: 5/10 increasing every 20 minutes:
5/10
10/20
15/30
20/40
25/50
50/100
75/150
100/200
150/300
200/400
300/600
400/800

Our tournaments last 3.5-4.5 hours and rarely even make it to the 400/800 level.

How many tournaments have you run that were "too long". Also, what is your definition of "too long".

If 3.5-4.5 hours is "too long" you don't want a poker tournament, you want to play bingo.