I'am very interestinc what you talk about KWh meter.
Please can you explain me more detail about the project.
I build digital kwh meter to graduate from my univ. This kwh meter able to sampling in 20000 sample/second.
And able to communicate with PC RS232 asynchronously via data packets. And also has hardware address (like MAC address on PC) so, every kwh meter are distinguishable.
Actually, build kwh meter is very easy right now, since many company have produced specialized IC for such purpose.
I used MAXQ3120 on that project, this IC has build in high resoulution ADC(16bit-Deltasigma), MAC(high-speed multiplier),and RT clock. but now this part has been discontinued. (I don't know why maxim stop produce this).
By the way, u also can use microchip MP3905 with just 0.1% error rating, and price under $2. But this IC is not microcontroller, so you need microcontroller addtion to process the data.