Is there a history of new betas running slower as they are released. In other words, could the next beta run slower/take up more resources? I think I'll wait on it a couple of days, when it's released. This beta has pretty much revived my mid-2010 Macbook Pro, and I'd be discouraged if Beta 2 slowed it down!
From my experience in the last decade, almost all betas stabilized over time, and they rarely improve performance in a big way, after all we're talking about 2-3 months for a complex OS update. I do recall during one time in iOS 8 or 7, beta 2 or 3 changed the animation timer for the worse and it felt slower. The system wasn't slower, just the animations were longer.
Apple did cut the animation timers for El Cap but the question is, can they lengthen it over time? Certainly.
I dislike animations, they're great for feedback and new things but over time, you just don't need it anymore, they just become pointless over time. I wish Apple would reduce it more on both iOS and OS X or gives us the option to kill it completely.