The hardware timer was set to 0xFFFF, then a simple loop ran for 250,000 iterations reading or writing on the given address range. Since the timer counts down, higher numbers in output represent faster operations.
From this, we can learn a few things:
* Writes are faster than reads, which is expected with write buffers
* ROM accesses with the wait controller set to 1 wait are the same speed as RAM accesses
* VIP accesses are slower than anything else
* The slowest VIP write is faster than the fastest RAM/ROM read
I also ran the test using cartridge RAM memory rather than ROM. It's configured as 1 wait permanently in the hardware, and sure as beans, SRAM accesses are the same speed as WRAM accesses. Don't be afraid to use your cartridge RAM as scratch memory.