Speaking of lengthy Sevenths, I recently discovered Leif Segerstam's 1991 recording with the DR SymfoniOrkestret on Chandos. I love it. It clocks in at 1hr 28mins, but Segerstam conducts superbly, and the orchestral performance is top of the line. The first movement is a beastly 25 minutes, but the tempo relationships are ideal for me. The Nachtmusik movements are certainly on the slow side, but they can justified be in the right hands; here Segerstam conducts with an excellent sense of fantasy and atmosphere. The finale, at a whopping 19 minutes, is actually paced exceptionally well. The ritornellos are at a similar tempo as Stenz, and the episodes are like slower light dances. The final peroration is huge and satisfying. I'd recommend a revisit of this recording if you've forgotten about it.
As for the Klemperer, I also can't do it. I am fine with slow recordings if the tempo relationships can justify it (as is the case with a lot of the Chailly recordings), but I don't like slow just for the sake of slow. Actually, I do really like Chailly's slightly lengthy Seventh, but the finale is a bit too homogenized for me too, like the Klemperer. Incredible first movement though.
Erik