Bill Legall of Millersound in Lansdale, PA whom Will (tubegroover) and I mentioned, had 2 pairs of IRS V in his home, in different rooms. And he's had 2 or 3 pairs of Betas and several lower iterations in another room in the years since. He did sell one of the IRS V, the ones I mentioned having the flawless, mirrorlike finish. Personally, I would have kept those, as they were one of a kind. And if this doesn't sound completely ridiculous, the other pair looked pedestrian in comparison.
How do the IRS V and Betas compare? Well, as you can imagine from their huge difference in size, they likewise sound as different as that. I've not listened to Arnie Nudell's Genesis take on the IRS V, but I can say there is NOTHING else I've ever heard that sounds at all like them. Obviously, huge in every way, but with a relaxed liquidity you may not have expected. That said, over the years I've evolved to a place where I find larger than large loudspeakers fall down in the areas of imaging, especially, in relation to height. The IRS V do exhibit very good timbre / tone, and the sort of naturalness that we aim for. Apart from imaging and the ability to site them in most people's room, the IRS V better the Betas. That's a bit interesting, because I have found, somewhat counter intuitively, so often in this business, the sonics of a brand increase for the better as you move down their product line.
Of course, take all of this with the grain of salt that Bill leaves almost nothing stock, and works his magic on more or less everything that exists in his life. So, how far does the typical Infinity come? Unfortunately, I can't really say...