"There are a few problems that can arise when using Keil C51 (and other) printf() routines."

Indeed, however these are well documented in the manual.

"Firstly printf() is genuinely stack intensive and falls over if you try to pass it too many variables and pointers."

How 'stack intensive' do you think printf() is? Note that printf() failures caused by passing too many arguments are not related to its stack usage.

"ie printf("lots of constant info %d, 5); // should work
printf("lots of constant info %d ,%d, %d, 5, 6, 7); // doesn't"

Those examples will both fail, but not for the reasons you have given.

"Also, genuinely stack intensive functions tend to fall over a bit when stack space gets lowish. I would tend to think that your LCD driver is pushing you over the limit, and that it's time to shift some variables out to idata or beyond."

If you're running out of stack space the last thing you'd want to do is move variables into idata.

"Have a peek at my LCD code if you think that will narrow it down some also"

You need to fix your delay function.