Fear not. Your performance concerns are mostly unwarranted (creator or Velocity here). Here are some articles to consider reading that help debunk this myth:

http://css-tricks.com/myth-busting-css-animations-vs-javascr...

http://davidwalsh.name/css-js-animation

http://www.sitepoint.com/incredibly-fast-ui-animation-using-...

http://www.smashingmagazine.com/2014/09/04/animating-without...

https://developers.google.com/web/fundamentals/look-and-feel...

For what it's worth, Velocity is a fairly new library. I wouldn't have gone down the path of JavaScript-based animation had my research and testing demonstrated that it was appreciably inferior in any way.