I am using the 13lb springs from RSD. If your track is not really dusty I wouldn't go any softer. The green AE are 11.5lb. If you have grip roll go softer, if not try harder (springs)
In the end it is not so easy to recommend from far away. In doubt, try it yourself. Suspension dynamics are very complicated and hard to predict.
Some more words to my steering conversion:
1. It works pretty fine on track!
2. For maximum precision you need to get rid of all the slop in the steering assembly, because the link from servo to steering brace is changed from servo to steering arm. In my case the original kit shims are 0.3mm too short and the bushing too long. This leads to little, but disturbing direction changes.
Nevertheless, with these changes plus just 1mm shims under the arm mounts all around, I could better my personal best around 150 thousands of a second