Many thanks for all your replies.

Michael - the Cygnal parts look good, the problem is that this project requires a direct drop-in replacement for the Atmel AT89S53, 24MHz 44-pin PLCC device.

The project was designed a year ago, for various reasons a PCB redesign is out of the question. I have been tasked with getting better performance from it, so my first port of call was of course to look at increasing the clock freq. I have access to the source so I can tweak any time-critical code if necessary.

The DS89C420 is pin compatible as far as I can tell, so seemed to be the best option - at least if I could clock it at 50MHz (incidentally this is what the news article refers to, rather than using clock doubling).

I am interested to know if you are aware of any other pin compatible parts, or any technical contacts I can speak with at Dallas/Maxim about the 50 MIPS part. So far all my email queries via the Dallas/Maxim websites have gone unanswered.

regards
Robin