SnGs - When do you move up?

[Aequitas58]

I killed playing SnGs this weekend. I was playing $20+2s and $10+1s. On another thread, Defendant said he likes a bank of at least 10x buyin to play a particular SnG limit.

Forgetting about ring games, when do you move up in the SnG world? Do you randomly give a higher priced tourney a shot or do you wait until you've built the money to play at that level?

Also: Could anyone w/ experience tell me about the skill level difference b/n the $20+2 vs. the $30+3 on Party?