As some have mentioned, the best thing is to borrow the devices you want to consider and audition them in your home in your system. As I have posted many time before, spending that kind of money, dealers should allow you (with credit card on file) to take equipment home and audition it in your home. If they will not do that, then I would shop elsewhere.
Establishing good relationships with dealers is key. Once they know you, and know you are serious, it shouldn't be a problem for them.
Over the decades (sigh!) I have established pretty good relationships with dealers that allowed this.
But, back to the topic. In earlier posts I have mentioned that I have gone from Audio Research SP9, SP9MKII, SP11, REF3, REF5SE, REF 6 to REF10. I have listened to the SP9MK II (retubed) vs REF 3 and it was enough of a positive difference that I purchased the REF 3. Also, remote control helped.
This is the way my sneaky dealers (Steve at Stereo Design in San Diego, retired now) and Randy at Optimal Enchantment in Santa Monica (retired, but taken over by two knowledgeable partners), operated. They would allow me to take equipment home (with a stupid grin on their faces), knowing that if there were enough of a positive difference, I would probably purchase it.
So, I was interested in the difference between the REF3 and REF 5 or REF5SE. This was before the REF 6 came out. So I took them home. Not enough of a difference between the retubed REF3 and the REF 5 to warrant the purchase. But, the REF 5SE was pretty darn good. So I bought it and sold my REF3.
Then I magically took home a REF 6 and big difference too me between the REF 5SE and the REF 6. So I bought the REF 6 (reviewer's copy) and got a very nice trade in price for the REF 5SE so that I was hard to pass up.
My (so far) ultimate goal was the REF10 which I heard several times, but the price was wayyyy too much. Until I got a demo unit from Randy for a stupidly low price and a great trade in price on the REF6.
Anyway, seriously, I loved the SP9MKII, it has an outstanding phono Section. Same if true for the SP15. If you can grab one, do it. That is an outstanding pre-amp period. I could actually live well with a REF 3, REF 5SE or REF 6 and not miss anything in sound quality. Those are great pre-amps.
In my opinion, when you get to that level, you might hear differences in sound, but (too me) I have not heard night and day difference. It just is slightly better.
Honestly, If you have a decent turntable, and a not so great phono stage, get the SP15. However, the REF3 with a phono 6 or REF 2SE phono stage is hard to beat.
As far a Conrad Johnson is concerned, they make excellent products. But, you have to take it home and demo in your home in your system.
Also, one last thing. Many people make the mistake of simply swapping components and listening. What should be done is listen to your favorite song with the original equipment and the level you like. Then listen to a test CD and measure with a inexpensive audio tool or DB meter that level. Then swap equipment and place the test CD in again and adjust the level so it matched the original equipment's sound level. Then listen critically.
Many people mistake differences in sound level to mean better or worse and that is just not true. This is where the "I heard a night and day difference) usually comes from. When in actuality it is just a level mismatch.