HI,
Since you are most likely going to use your medium mics with the new good pre as well, I would audition all your mics with a good pre,
then after you get the good pre, get a good mic that works with your good pre.
I can't see you doing the opposite, auditioning medium pres with a good mic?
That's what I would do...I used to be and still am in your same shoes...
I eventualy got an AMEK/Neve dual pre 9098 and it is awesome...makes all my mics sound great...
then i got a nueman mic!@
there are allot of good pre's and mics out there..what ever works for your style./budget.
good luck