Overall the MIrage is in the top 3 or 4 turn fighters in DCS IMO. All the planes do different things in different E states, speeds, AOA, etc etc. Remember you're fighting AI as well - I'll link (or do a search) for the Folds of Honor tournament this year and last, and there are a lot of Mirage vs F14 fights where the F14 pilot easily manhandles the Mirage IIRC, and a few the other way as well.
The 30mm w/Mirage has a much poorer trajectory than the 20mm in DCS, you have to lead a lot more with the Mirage than every other plane except the JF17 I think.
Lots of the best pvp DCS players flew in last year's and this year's Folds of Honor tournament. Lots of great F14 vs Mirage duels, go to 10:00 or so and see where the F14 beats the Mirage once they end up on the deck - the F14's turn rate and radius are insane at certain airspeeds, both IRL and in DCS - it'll easily out turn the F15 down low, give the F16 a run for its money, especially under 400kts, as well as everything else under certain conditions.