Currently our transcodes ship the original frame rate except for 160p which forces to a max of 15fps.
48/50/60fps videos look great but usually aren't necessary and waste either bandwidth or quality and CPU time; most 50/60fps videos I've come across on Commons just happen to be from high-quality originals and aren't demonstrating high-frame-rate goodness.
Consider cutting the frame rate in half on transcodes of >=48fps sources.
I changed my mind and, in recent updates, instead added extra bandwidth for the higher-frame-rate videos so they still compress nicely.
(Except back-compat MJPEG output for old iOS devices is decimated to 30 to avoid bloating the rate.)
When using adaptive streaming (on iOS now/shortly, and on other systems in future) low-bandwidth situations should automatically pick based on available download speed and will just bump a resolution down if they need to.