"No, with C in order to achieve the efficency of assembly language you would have to define all variables as single byte integer variables."

Ok, that makes sense - I would always use "unsigned char" in preference to a larger type if it were big enough.

"I find that when using subroutines in C, that they use much more stack space."

That certainly isn't the case with Keil - local variables aren't allocated on the stack. I can't comment on other compilers. What compiler do you use?

"No, the RAM is external after the 255 bytes of idata space."

Ok, I take this to mean that it can't be used as stack?

"With C, you can define where the stack begins and ends."

You can't define where it ends - the end of idata determines that.

On the other hand, are you maybe talking about a software stack in xdata rather than the cpu stack?