Ron, for many applications, the full capabilities of the ACS600 are overkill but, over 50hp, it doesn't really cost anything extra to include them. At that point and up, the ACS600 has always been a pretty competitive drive even on fans and pumps. Plus, with DTC's superior torque producing cabilities, I'm often able to do the same job with a one-size-smaller drive which makes it even more competitive.
The 600 will still be available until about the end of the year. After that, service parts will continue on for many years. Even now, the prices of the 600 are gradually rising to push new applications toward the new 550 and the 800.
The 800 is, for all practical purposes, a 600 in a smaller package. The software looks very much the same and the control terminals look the same too. The only real change in IO is the addition of a Digital Input 7 at the bottom of the X2 strip. It is permanently assigned as a Run Enable or "safety loop" function. Several industries, especially automotive require either contactor release on an E-stop or a programmed input that is NOT software accessible. The new input is in response to that need.
The only substantial changes in my opinion are: integral brake chopper included in all units under 20hp, startup and tuning wizards for just about everything (I never use these), and PLC-type logic modules that can be used to create all kinds of unusual timing, boolean, and comparative operations on internal drive functions as well as the ability to use any spare drive inputs and outputs for process control unrelated to drive operation. This is called Adaptive Programming and will be a big deal with the systems people but, for us ordinary blokes, I don't think it will be used very often.
For bells and whistles, there are: space inside even the smallest drive for two option modules and a fieldbus communication module, a larger LCD display, and, on the digital inputs, the option of setting up Run Forward, Run Reverse inputs. This was not available on the 600. There are also some new choices to make the creation of a nice crisp jog a lot easier to set up.
And, for those simple jobs, you might want to look at the new ACS550. It replaces the 400 but extends all the way to 400hp. I expect a lot of the higher hp 600 applications to go to the 550 rather than the 800.
And, for mrdegold, I would sure like to hear about any conclusions that are reached on the IGBT failures. I routinely use 600's well into overload and don't recall even having a failed IGBT. Something peculiar must be going on there. (I seem to gravitate to stamping press and forging hammer drive applications and these drives usually go to 160-180% overload for a short time on every cycle!)