Heavy transport category aircraft are authorized to exceed the 250KIAS limit in the climb below 10,000 MSL when required to maintain a safe speed margin in clean configuration.

Military fighters do the same and often climb out at 350KIAS below 10,000 MSL. Many jet fighters descend at 300 KIAS below 10,000 for the same reason having the ability to maneuver while clean.

IR routes for military use are often used in VFR weather. VR routes require higher weather mins to used.
Speeds in a IR/VR route and MOA can routinely exceed 500KIAS to .99 Mach. at altitudes down to 500ft AGL.