A-arm suspension travel capabilities are determined by overall outside-to-outside wheel width and control arm length. Maximum travel from a car that is at or near maximum width allowed by SCORE is about 30 inches. But this can be, and usually is, affected by where the lower control arm attaches to the spindle, tire diameter, chassis requirements, vehicle weight, etc. In practice, 27 to 28 inches is about it. This is particularly applicable to front suspension because A arm suspension works so well. It's one of the few things on a modern car that isn't lame (addressed on a previous thread). Please know that there are strong yet simple suspension systems besides A-arms for the rear which are capable of significantly more than this amount of travel. So, the competition with solid axles is far from over.
<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>