If you want or need to burn some gain then you might look at a B7-8K
or a B7-10K.
In many preamp or line level apps--- the secondary is either very lightly loaded or not loaded at all (i.e., intentional loading). When this is the case it is the primary L that effectively provides the load impedance that the anode of the tube is looking into. The stated primary impedance under these conditions can be moreso viewed as an alternate way of stating the voltage ratio (i.e., turns ratio)--- and the user might be moreso governed in their selection of which "nominal" impedance is best by considering what they want or can do with their voltages--- how much step down do they want or need.
You still want to pay attention however to the MOL listed for each primary winding.
Hope this helps.
MSL
Builder of MagneQuest™ & Peerless™ transformers since 1989
