What is considered to be a reasonable temperature rate change in a HERMS or RIMS system?

When brewers speak of their mashing techniques using mash temperature controlling technology, they sometimes make claims as to how fast they can get their mash from temperature 'A' to temperature 'B', and brag about the steepness of their 'ramp' (and sometimes forgetting to mention overshooting their temperatures). What I would like to know is what is a reasonably quick ramp (in, say, degrees F per minute), and what is a ramp that is really too slow as to affect the conversion process in a negative way, and what effect that slow ramp would have on the final product. Let's presume we're not doing anything really fancy, but maybe a protein rest, or other commonly used rests.