Question for tube aficionados

And almarg has stated an important point about the use of the 5751 variant in your CJ preamp...
Please note: The indiscriminate substitution of type 12AX7 tubes for the 5751 will seriously degrade the sonic performance of the unit.

The 5751 has lower gain, so it's recommended to stay with a 12AX7.

This comment is backward. The book is saying not NOT to replace the 5751 with 12ax7. The higher gain of the 12ax7 would overdrive the circuit, being 30% higher. That’s why it says not to indiscriminately do that.  

I have a used the PsVane with much sucess.
I have an Amp that uses the 12AX7 In that I have put Sovteks (Basically nothing more than a tube to put in a tube socket) 
Also put in Vintage Mullards and Tele's . The matched Set Psvane to me sounded better balanced, clearer and detailed.
The Mullards a little bright & the Tele's A little to creamy for my system.
 But it is always specific to equipment.
I also had a tube phono section which required both pairs. Again I tube rolled the Sovteks and
only replaced with the PsVanes. Vintage is great but they have their issues.  With the PsVanes were very quite and for the price worked great and you should have no regrets. At worst they become a very good back up set just in case your vintage choice go south. But now my vintage 12AX&'s are my back up and the Psvane are still in and working fine for well over 2 years.
Lastly give them a little time to break in. Out of the box you will know you are the right path.

I have Shughang Black Treasure 12AX7LS and they are mostly better than Telefunkens. Tighter, cleaner bass, clean bright sound without glare and sweet highs. Slightly reduced air.