The DVD of Haitink/BPO doing M3 is much better than the studio recording. On the studio recording, the cymbal player lands about three or four prominent crashes in the wrong spots - it's very obvious (first movement). Sylvia McNair is very good on Haitink's M4; both on the studio and live DVD performances. Haitink/BPO doing M5 is decent but has the slowest Adagietto on record. For me, there was nothing special about his Berlin M1 or M7. If you're going to get Haitink/BPO doing the 7th, get the DVD. The Haitink/BPO M6 was dull and prosaic in the first two movements, but excellent in the last two movements (S/A order). It truly has one of the best finales out there, so it might be worth seeking for on the used market. However, I always thought that Haitink's first Concertgebouw M6 was a tad under-rated. It definitely has a better scherzo than the Berlin one.
For M3, I would either wait to hear Haitink's new CSO one; get the 1966 Concertgebouw one (with Maureen Foresster), which has just been reissued in excellent sound; or get the live Berlin one on DVD. I would skip the Berlin studio one. For M5 and M6, if it's Haitink you must have, you might want to consider his latest incarnations with the Orchestre National de France. The 6th, in particular, isn't bad. I believe that those are on the Naive label. Haitink made two recordings of M1 with the Concertgebouw, of which the second one is clearly better. Unfortunately, that's been out of print for quite a while.
You asked about Haitink's 1982 M7. I'm not a fan of that recording. The first, second, and fourth movements are very good. But the scherzo is the slowest one on record, and the finale is just too poopy for my taste - lasting well beyond 18 minutes. I also find that it's very weak in the bass end. I like Haitink's original 1969 recording of the 7th much, much more. I'm told that the Christmas Matinee Concert one is also really good.
If you bother with Haitink's 8th, you'll want to spend the bucks for the Pentatone SACD/CD hybrid issue of it.