It's been a while since I've posted... I am very busy these days. :-(
I am currently playing with SiLabs C8051F344 with a purchased copy of Forth Inc's SwiftX (under Windows -- my Linux development effort never fully cooked).
I am impressed with the speed of this "lowly" 8051 derived 8-bitter. It isn't meant to do big things, but for small things it fairly rocks.
I've previously played with the C8051F93x very lower power MCU, but given my current interests (GPS tracking), the difference in power consumption between that very low power part and the more power hungry F344 is minimal. The GPS consumes so much current when running that the MCU is just "noise" in any power chart plots.
When asleep, the difference between consuming 1uA (sleep mode) on the F93xx vs 25-50uA on the F344 (clocking way down to around 40Khz) is not worth considering (we are talking years of battery life for either).
More on my current project later... but for now I am just enjoying crafting Forth on a 8-bit MCU :-)