In my experience the Zilog Encores are worth investigating,but there are some reservations.
The chips.. on a 20MHz clock they are rated at 10mips ,but 6 or 7 is more representative ,with an extensive peripheral set.(The Atmel AVR is upto 4 times faster due to its pipelining and better architecture)
I did not have any noise immunity related problems..but there are question marks on wether they are a good as the Atmel in this area.
This could be due to bad design at 3v on part of the complainant..

I love the single pin debug with simple rs232 interface board and the ZDS11 C compiler and IDE work well together,shame that no 51's have this at the same price.. Silabs are good but way to expensive.
There are significant reservations on the ZDS11 compiler and the quality of its output.. quite buggy and inefficient..Its not highly regarded ..File and library Formats change often.. Knowledge of asm is a must..
The "scene" for the Zilog is small and dwindling, and it doesnt look like Imagecraft or others have any intention to make a good quality compiler, as they have for the AVR.

Rob