No doubt about it, the SiLabs MCU's are the fastest. For one thing, the DS89C4x0 series UART works faster than the SiLabs UART, under some circumstances. It can be encouraged to work at the oscillator frequency, which the SiLabs part doesn't (which influenced my decision, on one occasion, not to use the SiLabs part). There are lots of things that influence how "fast" a part is, aside, simply, from oscillator frequency. In some cases, it is a built-in feature, and in others, it's a coincidence of oscillator frequency and timer/UART interaction.

There's no question that 100 MIPS is going to execute more cycles than 33 MIPS, but if you can make the DS89C4x0 synchronize precisely with a physical process it can reduce the number of instructions needed to perform a bit-banging operation, for example, significantly. 33 MHz, BTW, works fine to produce a 57.6 kb UART if you need one, and that's with the same firmware as you'd use to produce 19.2 kb from 11.0592 MHz.

Most importantly, if it has to fit in a PLCC-44, or a DIP-40, as when you're upgrading an established circuit, or if it has to use 5 volts, the SiLabs part simply won't fit.

BTW, I do agree that the SiLabs develpment kit is probably the best place to start. It's too easy-to-use to pass up, and there are none of the ATMEL "gotchas".

The SiLabs parts are very interesting, but ... there's a long and steep learning curve, whereas the DS89C4x0 just plugs in and runs ... not always the way you might hope ... but it does simply take off and execute the code. The ISP via the serial port is quite straightforward, too. If your code uses autobaud, it will easily find a suitable baud rate, and you're off and running.

RE