I wonder what Star Trek directed by Quentin Tarantino would look like...

If you're a big Japanese OEM, you can get some SH7785 (600MHz SH4a)
which apparently perform quite well for their low power consumption
(however outside of Japan it's apparently damn near impossible to get
  newer SH chips. We've tried and failed to even get a roadmap from
Renesas Europe)

Renesas is refocussing on multi-core chips instead of higher clocks
(IIRC the SH-X3 is a quad-core design and already running linux)