SSBO get block of data instead of iterating
yes, and no. Loading the floats into the SSBO is loading them for the shader so yes you still have to iterate over them. And GPU's generally are good at latency hiding so whether or not you read floats or vec4's the GPU should be able to read them in just as fast. But processing them as vec4's instead of 1 float at a time will be faster since the code is taking advantage of the GPU's vector processing.