I'll do my best yet again trying to explain why neither Maiku or RK12 won't get you anywhere in c12 or c414 builds.
First of all, asking such a question is exactly the same as: What amplifier can get my Stratocaster to sound like a Les Paul. Answer: No amplifier can achieve that.
The capsule is your guitar, and it's such a shame to waste so much energy into creating wonderfull circuit replicas(amplifiers) with accurate transformers, fets, layouts, bodies, bias points, and in the end use wrong type of guitar.
More or less high end on that RK12 (Maiku, AA, Røde...) type of capsule is determined by the volume of the holes under the diaphragm. It does not mater if you achieve this difference by using EQ or by altering the size of the holes. Paying extra for 2db of HF is paying for turn of the HF knob on an eq. It is the acoustical principle of the capsule that matters regardless of frequency response curve.
By far the best capsule of this type is produced by Rode, and it is found in NT2a, K2, Classic II... it is exquisitely well matched from piece to piece, and front to back. It is not hyped in HF at all, it is almost flat in response. The difference between the Rode models sound comes mostly from headbasket.
However, i've never heard anyone comparing Rode models to c414. So why put this type of capsule in a c414 or c12. In the end you will end up with a Røde mic no matter what circuit you use.
If i were making a c414 inspired mic(and not have CK12) i would try to get my hands on used c4000b, swap the capsule, sell the c4000b with "upgraded" rk12 type capsule and use c4000b for my build. You would need to mod the Akg mic to add polarizing voltage. If you don't need patterns c3000b is great too. Those two mics sound "bad" because of the built in Eq, not because of the capsules. There are also other inexpensive Akg models with similar capsules. The fact they are electrets don't change anything, the material is deposited on the backplate, doesn't affect the performance, and applying pol.voltage to these doesn't change anything.
How to test this without serious testing equipment?
Take Neumann u87 and just about any other mic with 34mm k67. Place them in front of a monitor, at the exact same position, and record pink noise under same exact conditions. Then run EQ Match and match the two recorded files. I promise it will be almost impossible to hear the difference.
Now repeat the same test with two mics that have different construction. Say original c414 and a mic with RK12 equiped capsule. Run the EQ match, and you will get the same exact frequency response while the takes will sound different! You will hear something that many characterize as 3d effect. One will be more 3d.
This is because of how the physical and acoustical principle works and sums 360° of sound into one mono take. The more room in the sound you have the more obvious. This is why i like to test my mics as drum rooms. It's super revealing. Vocals are contrary to what many would think quite poor shootout sources. Low spl, recorded in booths, don't go low, and are relatively poor in harmonics. Slow, and soft transients.
This would be a 1 dimensional, static test. If you start moving the mics around you would see how differently constructed capsules change the 3d response in regards to proximity effect, and off axis response.
