It's very interesting. When animating from 12 to 34, we'll animate the 2 through 22 digits to reach 4. However, when animating from 12 to 3004, we don't spin the 2 through 2992 digits. Instead, we skip digits artificially based on a target frame rate. (Since the animation is supposed to take 2 seconds, at 60fps we have 120 frames to show those digits, so you're not going to see all 2992 anyway.) We originally set this target frame rate to 60. We recently dropped it down to 30 in an attempt to improve the perceived FPS in Chrome. (See https://github.com/HubSpot/odometer/commit/fc5ca1572d0ad218c...)

We'd certainly love to hear from the community if there are any other approaches worth trying. For those interested, we have an issue tracking rendering performance here: https://github.com/HubSpot/odometer/issues/3