I've asked a VC this question before. They said that in theory going after 5-10x returns sounds great but in practice no successful VC firms use this strategy. They all make their money from the few who "return the fund".
A friend of mine who graduated with honors from an Ivy econ program moved to Palo Alto and went into PE. I asked him why he didn't go into VC in the heart of venture capital.
He replied that PE was as close as you could get to formulaically printing money while seed-stage (and even later) VC was more like splattering paint at a wall and seeing what sticks, and that the former suited his personality better.