> we just want to see what is faster as a core
You apparently did not understand my point.
There is nothing like "faster" in processors; or, it depends on your definition of "faster".
So, define "faster" first.
> There are opensource compilers for all of them
What compiler are you talking about? C? Does this really matter? How do you intend to use it? As a control/monitoring core, it does not need to perform complex tasks, does it? Setting up a couple of registers, sitting in a loop and blinking some LEDs - that's not really a task for which a HLL is necessary. ... What do you mean by "maturity" of a compiler?
Have fun!
JW
Added after 7 minutes:
> my feeling looking at the ISA and
> architectures is that they are pretty similar
One more thing. You might not know the history perhaps - both the 6805 and 6502 originate in Motorola's 6800 and which was a general purpose 8-bit processor. The success of 6502 resulted mostly from the handcrafted design which resulted in a very small transistor count, which was important in times when transistors were large and silicon area was expensive.
On the other hand, 8051 is a completely different story, originating from the 8048, which was a dedicated microcontroller from the onset. There are peculiarities in the '51 - for example the register banks, bit operations - which might make it a bit tougher to implement, but make a small embedded designer's and programmer's life easier.
JW