[WarBus]

It all depends.

Option A. $2k - The gambler.
You want to take a shot. If you run hot your roll will be over 3k quickly. If you drop 500, drop down.

Option B. $3k - The risk taker.
You have the minimum roll. Give it a try. If you drop to 2k move back down and try again when you have 3k again.

Option c. $5k - Conservative.
You have a large roll for your current limit. You can take a shot at 5/10 and still have plenty of $$$ if you do poorly and move back down.

Option d. - $10k
For those who are:
Too stubborn to move back down.
Unable or unwilling to ever add more $$$ to their bankroll.
Use poker as a source of income.
When your roll is very large, the swings have a lesser mental effect. You still have a very large roll if you move back down. You can take a bigger shot at moving up which gives you a better chance of adjusting to a new level.

These are just examples and everyone has their own unique tolerance for risk. You just have to know what size roll is best for you.

I normally maintain at least 1000+ BBs. A big roll allows me to play my best and not worry about going bust.