[ModMustang97GT]

Do not get coil overs in the rear. You can't get a soft enough spring for the rear coil overs to keep the ride comfortable. MM states flat out that you should not get rear coil overs if you worried about ride quality. For drag racing and ride quality you will want a not so stiff spring in the rear. Your eibach springs are plenty. I would get coil overs for the front and then get a set of either the matching eibach schocks to your springs, or go with some adjustables.

The Tokico illuminas are the best drag adjustable out there. You can set them great for the track, then dial em back a bit for the drive home. Also, do you have subframe connectors? I would recommend a good set and front coil overs with a 250 lb/inch spring, something pretty soft. It will still handle better than your stock springs because they are coil overs, and they will work together to give you a MUCH smoother ride.

The ride quality is really directly from the spring location on the arms. Your springs are around 650-700 lbs/in but because of where they are located. You feel the harshness of a 700 lb spring in the ride, but you only get a 200-300 lbs of force at the wheels. So you get a harsh ride with poor wheel rates. Coil overs fix that. 300 lbs on the body (less stiff than the stock springs for harshness) and the same 300 lbs on the wheels.

 

[ModMustang97GT]

He;s looking straight line though. For drag racing, you can still have some semblance of ride quality with decent performance. It sounds like you are not the trailer queen type racer, so you should be able to get away with an upgraded set of lower control arms, springs and shocks. And some front coil overs will make the front lighter and have better performance on and off the track.