Herb,
I think you're decision to use the Bertini recording - in lieu of the more famous Mehta/VPO one - because of the differences in sound quality underlines a very important point. Many people want to believe that, just as the case is with Beethoven, Brahms and Bruckner, that the 'golden age' for Mahler was sometime in the past. But I always argue that NOW is the golden age for Mahler, and it may get even better in the future (the predicted drop in interest doesn't seem to be happening). That's basically for two reasons: first, conductors and orchestral musicians are far more familiar with the music than they were in previous decades. Young musicians coming out of music schools and conservatories have to know their Mahler excerpts backwards and forwards. Conductors are being judged on their Mahler pretty much every year. The second reason is because of the obvious improvements in sound quality on recordings (and downloads - I won't forget the downloads).
I've had a number of people lecture me that 'sound' isn't that important in recordings. I always reply back, "funny, I thought music WAS sound". That's an obvious point that holds particularly true for Mahler, Shostakovich, Stravinsky, etc. All of this is to say that I think you made a wise decision, even though the Mehta may be more of a sentimental favorite with you (and truth be told, the organ and percussion are not all that great at the end of the Mehta recording).
Also wise was your decision to not over spoon-feed your guests. Good job and congratulations.
I once belonged to a listening group here in San Francisco, where one of the members had great success playing the Blomstedt version of Mahler 2. Then again, that recording - one that I like, by the way - involves our hometown orchestra.
I once finished off a listening party - one where I was choosing the music - with just the "Blicket auf" and "Chorus Mysticus" sections of Mahler 8 (the ending, in other words). The ones who liked loud music loved it, but some of the others weren't so enthused. Then again, we had a strange mix of opera queens, modern music mavens and early music buffs. It's a wonder any of them got along at all.