best 4.5" midrange drivers under $1K

12Ms are great drivers but it cannot match the quick transient of my ribbon tw. I guues its because of its paper cone. thanks for your input :) anybody else

I am not sure - those are pretty extreme specifications - do you understand what you are asking for?

This is the only thing I can think of that nearly meets your specs is ACCUTON C²79-6.

I would not design around a tweeter.

I'd start with midrange first and then find tweeter and woofer to match.

Sure, AudioTechnology 4 & 5" Flex Units. They are poly cone and run $240-287 each and most important, you can run full range with no x-over to over 5Khz.
You'll need a 3rd order x-over @6Khz for the 4" unit.
If you make a pair, can I come over and listen?

If you use accuton that low then I'd use two per speaker.

I assumed you wanted metal/ceramic instead of damped designs like paper/poly/fabric.

Another option Jordan JX92S - this will be comfortable in the range you require but it will roll off a bit in dispersion above 2 KHz.