Mostly using the MIS at the moment - seems middle of the road in all departments, save if I need to, I can launch a belly full of missiles at anything red on my radar.
It's a nice ride and no mistake and is nimble enough to make its weapons useful...
For me the connie is too slow at turning to be able to bring those 4 s4's to bear on the buttnuggets who harass me when I fly it, but the ability to carry a rover is just too useful to me to be able to give up on.
I suppose for your needs, the Quantum speed can be managed by changing the component to the "best" one in its class, so putting that out of our minds, higher speed in standard flight, atmo handling and range... I'd say keep an eye on the Murcury for what that turns out to be, but if that's not a goer...
If it's purely to get from A to B as swiftly as possible with no regard to anything else, there is nothing faster out of Quantum than the Herald. After that it's the 350R and then the dedicated racers like the Razer and the M50 but you are losing a lot of ability there just for some poke in the go go pedal.
I've flown a 350R for years, it's a little drifty but still handles well and acceleration is off the chain. For a ship advertised as "the fastest ship you'll ever call your own" to be second to the Herald is a bit of a kick in the boxer shorts, but I'm waiting for Beta and balancing before giving up on the old bird, before the rework she was super fun to fly as a knife-fighter running rings around a foe but with each pass it got more and more drifty and less and less able to evade. Now we have the auto-aim it's one-shot city for this and the dedicated racers a lot of the time. Again, balancing needs to come along for that.