The reason I compared the 75 grn Amax in 224 cal with the 87 grn Vmax in 243 cal, is because bullets are of similar BC's - and that is the fairest way . In order to achieve the same BC bullet as a 75 grn Amax - you need to look at 90 + grn bullets in 243.
Your last post illustrates this point perfectly - - Yes the 58 grn Vmax in 243 can easily reach 3800 fps - but it only has a BC of 0.250 ( Brian Litz independently measured the BC at 0.238 )
Whereas the 53 grn Vmax in 224 cal has a genuine BC of 0289 - this means it flies flatter - and retains more energy at longer range.
I know I wont convince you - and I don't feel the need to try - But it is worth noting that only one of us can speak from direct experience of owning both the 22.250 shooting 75 grn bullets and directly comparing it to a 243'.
Mine is a unbiased opinion based on experience of firing thousands of rounds using both cals and if that not good enough, just plug the numbers into any ballistic program.
I am not knocking the 243 But the OP asked specifically about the 22.250 shooting a 75 grn bullet - your solution of getting a 243 in preference, wont give him any ballistic advantage - in fact it will be slightly worse ballistically.
Live long and prosper
Alan