best 4.5" midrange drivers under $1K

EJ Jordan JX92S 45Hz - 20K awesome driver and they've been at it forever.

If my understanding is correct, Feastrex has some odd prototype components sitting around from which they could put together a pair of 5-inch drivers that would surpass your performance requirements but would probably not quite live up to theirs, and thus could not be sold as regular Feastrex products. Feastrex drivers are normally beyond your price range but if they would agree to put together a pair of drivers using those components for you, you might be able to get them to give you a special price . . . I'm not sure if they would be able to accommodate you right away as their sales nearly quadrupled in the past year and if present trends continue they are going to be B-U-S-Y. But it can't hurt to ask, and if you are going to inquire, sooner is better than later as they are only going to get busier in the future, I suppose.

"EJ Jordan JX92S 45Hz - 20K awesome driver and they've been at it forever."

do you know the weaknesses that this particular driver has? Look insteresting but need to know what to expect if I try this

Audioism, according to your stated requirements, the JX92S should be an ideal fit. In regards to weaknesses, as far as a 5 inch driver is concerned, you will be hard pressed to find much wrong with the Jordan. They certainly don't sound like any metal based driver I have ever heard, musical without peaks or harshness whatsoever. Open, clear midrange and great dynamics to boot. These drivers are so incredibly versatile within their wide frequency range, just check out the specs. For better insight on various applications just browse the forums on diyaudio dot com. Good luck!