Did I hear MY name??
FMs are SO complicated in FA that it's not even funny! You can ask CAG about the fudgery I had to use just to get realistic AI cruise speeds and "Viking Departures"( but watching an AI F-15 Eagle do a verticle climb after take-off is worth it lol )
The drag coefficiants work in relation to thrust to weight ratios, so differences in one area affects the other. Your Saber is paying a much higher drag penalty in a turn than the MiG, compare your wing loading between the two and adjust the turn drag index cell accordingly.
If this is a MiG-15 remember that the 15 didn't have boosted controls and so would be harder to turn when fully loaded, so adjust your "Loaded" cells accordingly.
The A-4 model was a very baaaaad place to start, should have based both of them on the MiG and made the nessesary changes. Just using the max speed limit to restrict it will make it perform much more differently than a proper lope build. Each G envelope performance is modified by the next higher G, it gets complicated and I am lucky I have very strong hair roots or I would be bald. If you don't love spending endless hours in a low altitude turn to see where it finally settles out you will never have really good lopes.