This is just a theory but I would ponder that the likelihood of a VC's* success is directly related to whether they need to earn their salary or not. If a VC came into the game without needing a job, their decisions are more likely, in my opinion, to lead to homeruns than otherwise.
In my eyes, it's pretty simple. If fear of financial failure doesn't factor into your decisions, you will most likely make better ones, all other factors remaining equal. I am of course presuming that the VC is skilled in another way, which is the reason they were asked to be a partner at a firm. This means that they were either already an entrepreneur or something else along those lines beforehand. Very few partners worked their way up from entry-level position through to successful and financially secure partner (I only know of Fred Wilson). Further, and I doubt there is accessible data on this, I would bet that the VC's who came into their role with "fuck-you" money already in their account have generated higher returns on average than those with less personal wealth.
Fear is a horrible factor to throw into the equation when working as a VC. It forces you to do stupid things, like take too much equity away from founders up front or negotiate ridiculous terms into your contract. It also leads to mediocre outcomes as you are not investing in the edge cases that generate the real returns. You probably also end up selling too early and locking in returns instead of going for broke. Finally, you are impatient and not willing to let things happen. Go too many paychecks without returns and your partners get antsy.
What's the takeaway for someone working with VC's? Find those that have experience, play fair and are generally seen as good guys, have a track-record of success AND additionally a boat load of money socked away somewhere.
*By "VC" I mean someone at partner level at a venture fund.