When using SetFloatVectorArray() how many arrays can be set maximum to get maximum performance

a matrix will have 16 floats but how many i could achieve with SetFloatVectorArray()

(I know the number of floats is a multiple of 3...I dont really know...is it?)

another question: Can I inside a pixel shader method access the vector array like this:

float3 vectorArray[12];


//inside pixel shader
//......
uint4 t=Tex2D.Load(uint3(0,0,0));
float a= vectorArray[ t.x][ t.y ];
//.....