Do them all in 1996. Still quite obtainable and pretty much all of them did a good job, producing wines that are representative or at least connected with their classic styles.
1996 Pichon Lalande was great the other day. I always thought it was a bit atypical because of the unusually high Cabernet percentage but I realized I hadn’t drunk one since 2013 and opened it. Today, at least from a bottle that’s travelled to the US, you would never guess it was in any respect atypical for this estate. I wish I had cases of it, honestly.
Budget wise 1996 would be less expensive than 1989. I would add another wrinkle, and serve them blind in appellation flights and also include second labels of the First Growths.
I think an 89/90 or a 95/96 tasting would be fun; the vintages are different enough to keep things interesting, but the character of the chateau would still shine through.
I kind of like the showdown idea. I was thinking 89 vs 90 Montrose, but as already noted, Angelus ( ok, right bank but great) Lynch Bages ( I include that as a super here) and LMHB in the same vintages would be cool. Good pairs could be made for 95/96 also, I would think.
I see Palmer mentioned several times but that’s a 3rd, right?
I don’t think I’ve seen any recommendations for '86 Pichon Lalande (which I’ve had and is really good) and '86 Gruaud Larose (which I haven’t had but has a great reputation, and is a 2nd but not generally considered a “super” second). Both should be somewhat “affordable” - I’ve seen the '86 Gruaud at auction for around $150, which is too rich for my own wallet but should be in line with prices for other things you’re considering.
'89 Leoville Barton is also pretty great but is showing very young and would need decanter time.