What's your "diminishing returns" preamp choice?

@gmercer 

 mcintosh is amazingly pure, and damn near flawless.     Never owned, but hundreds hours of auditions.
 They are that good.
if you can swing, afford a good Mac pre, jump fast.

 Or try a couple different ones.

 It’s fun trying diff components and their signature sound, with your existing setup.

 Took me years to acquire what I have now.
30+ years 

If you can find one, the Ayre K-5xeMP is an amazing preamp for the money.  New it was $3500 to $4350 depending in the year but was brilliant.  You should be able to pick up a used unit in the $1800 to $2200 range depending on condition.  

I regret selling mine simply because it was such an amazing unit for the money.  I have added two units to my system since it left (PS Audio BHK and Art Audio Conductor) and they are both better but are quite a bit more expensive and the Ayre deliver 95% of the quality of the PS Audio and 90% of the quality of the Art Audio.  

Ok, so I still gauge diminishing returns against a venerable preamp I bought in the early 80's, the DB Systems 1b/2a/4b.  I've had it updated twice.  Other than a brief stint with tubes, it's my reference preamp.  The only reason I'm not using it right now is it doesn't have some of the features of the newer preamps.  I think I paid something like $800 in 1982 money for it.

I had a Thor TA-1000 MKII preamp that retailed new for around $11K. Having tried a number of different preamps over the years, I genuinely thought that the Thor was at the line of diminishing returns, and that it wasn't really necessary, sensible, or practical, to spend more.
That was until I heard the Allnic L-5000 DHT, which I now own. I didn't think there was THAT much more performance to be had from a tube linestage, but I was mistaken. Yes, the Allnic comes at a much higher price, but it's one of those rare pieces that make me think it was money well spent.
I'm curious to hear an Atma-Sphere pre and also a BAT at some point in the future. Perhaps the line can be nudged a little further still!

would be interesting to have a 'quietest' contest and then a 'musicality' contest between the benchmark and an ayre k5xe mp