Point well made Jimmy and you're right, I'm neither an Ampeg hater (quite the opposite actually) nor a "no mixed cabs ever" zealot. The current Mesa Subway line, which I am very familiar with, actually benefits from mixing cabs not only IME, but in the experience of many others according to their representations on TB. I also know that Hartke designed their 115XL and 210XL cabs to be used as a set - a buddy has them and they sound great when he plays them and I enjoy playing on them as well. I could go on, but I think the point is clear.
I tend to agree that any two
random cabs in combination, especially from different manufacturers, like say a 115 and 410 or a 610 and 112, are likely going to be a crap-shoot for a great number of technical reasons, but it could work out well. As an engineer my only general caution is to not assume that because say a Subway 112 and 115 or 210 and 115 sound great together, we now have empirical evidence supporting a position that any 210/115 or 112/115 combination will sound good together. In fact we can't even readily assume that any 115, 112 or 210 will sound good on its own.