It`s a not a common thing to use a rear anti-roll bar in a 1200 in the rear and in my opinion is a bad thing unless your wanting oversteer for drifting , But if you use a rear bar use slightly softer rear springs. This will give you Less oversteer in the middle part of the corner, and it will give you more forward traction. Another thing that's being used a lot is front Roll Center Adjuster Blocks to make the Front a higher RC , if you have stiff springs, or heavy damping up front, the initial reaction when you enter a turn will be very strong. In the middle part of the corner the car will probably understeer, but it's the initial reaction that gives the car a 'responsive' character. Roll center works this way: a very high roll center in the front will make the car turn in very aggressively, but understeer in the middle of the corner. It's nice if you like an aggressive car you can 'throw' into the corners, but I doubt it's the fastest way round the track. Conversely, if the rear roll center is set very high, the car will turn in very gently, and possibly oversteer after that.But the rear Roll center is harder to adjust being a solid axle.
if you combined with your stiffer springs (and damping) up front, and softer ones in the rear with no anti roll bar in the rear . This makes for a very stable car: it will turn in sharply at first, because of the stiff springs up front, but then, it will understeer a little, because with the stiff springs and heavy damping up front, it takes some time to transfer the weight onto the outside front tire. This happens a lot faster in the rear. But eventually, when the weight is fully transferred, the car will steer very well. This setup can be very fast: the car can be 'thrown' into the corner, without losing a lot of speed because of the mild understeer. Then,just before the apex of the turn, some lite braking / liter throttle will probably be needed, but after that the car will be very stable again under power , like in the entrance of the turn, which makes a high exit speed possible.

Other things to look at are ..
Driver Braking to hard too late ,
Narrow front track
Front tyre Pressures to high
Too much front Anti roll bar

Your Front spring rate should be ok (depending on your Front roll center hight as mentioned above ) Not sure on the rear spring specs . I would have a look at your lower control arm angle and try some Roll center blocks if the arms are flat or pointing up wards to the strut end and don`t use any of the of the drag racing hook up tricks on the rear .