yeah, it's all about removing those little gaps in the filament feeding route.

50mm's for any flexible is really good. :-)

I've got some stiff flexible pla that will print that fast, but for most other I usually go slower.

what actual filament did you use ?
Also what retraction settings did you use. presumably you didn't print the 600 parts 1 at a time. so retraction is essential to avoid webbing between parts.