The Philips XA should be the chip of choice. Where Intel with the 251 blew an opportunity to get a full performance improvement by staying 'object compatible' Philips took the full step and stayed only 'source compatible'. Sie... ahh Infineon has some interesting 16 bit chips, they, however, are only remotely '5 1 related.
The XA has a loot of very attractive features such as software interrupts (read hardware task switching) and a 16 bit bus if so configured.

Erik