Haven't conducted any tests, but I'm wondering where the "1 MHz without significant loss of resolution" info comes from. Looking at Table 29-16 of the ATmega328P datasheet they quote 2 LSB's (typical) of absolute accuracy with an ADC clock of 200 kHz, but 4.5 LSB's (typical) at an ADC clock of 1 MHz.
2 LSB's of accuracy is like saying the 10-bit ADC is really an 8-bit ADC. 4.5 LSB's is like losing another bit (almost). Is that a big deal? Depends on your application. In the audio world, 8-bit resolution is pretty bad but serviceable, while 7-bit would be downright annoying (to me). In other applications, it just wouldn't matter.
The Gadget Shield
: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons