Any pluses or minuses to the older McIntosh mc275 compared to the newer mc275's IV, V, VI?

The little LEDs under the tubes in the newer 275s are adorable and worthy of mention. Or maybe not, but it's too late now.

wolf_garcia, why is it to late now?

Having owned a vast amount of McIntosh, both "vintage" and new, including a pair of MC275VI's mono-blocked, I would submit that the more recent editions of the 275s are all excellent.  From my experience, unless you're buying new with its obvious advantages, precautions are essential to ensure that the used pieces are in the best condition possible.  Online purchasing makes that a challenge, so ask lots of questions and use a credit card that will stand by you in the event of a dispute over the purchase. I look for ads with lots of pictures that I can examine for any signs of abuse, are the tubes original or replacements, and I need to know the estimated number of hours on the tubes.  A concern for me are those ads that have one or two pictures (usually poor quality) and minimal descriptive narrative.  The newer editions of the 275 are extremely well-built, but abuse is abuse.  Since you're paying for quality, used or otherwise, that is what you should get.  Due diligence pays off.  Best of luck!