I performed this benchmark on WinAPE, after adding the following lines:
5 t=TIME
...
120 PRINT "Time: ";(TIME - t) / 300
WinAPE is cycle accurate, and it's using the internal TIME function. The TIME is incremented every 64 * 52 = 3328 microseconds, so the calculation for display should actually be (TIME - t) * 3328 / 1E6 = 38.904 sec. I will run this on my real Amstrad Plus today.
I can also run this benchmark on the BBC Model B. It could be at least twice as fast as the C64 since it's 6502 is clocked at 2MHz, and it doesn't lose any CPU states for video access like the C64.