sr20 > 4age
the way i see it is sr's are build to handle ~150kw and are designed to run a turbo
4a's are build to handle ~90kw and designed to run na
+ sr's are newer (i think)

and to make a 4age as tuff as an sr it has to be fairly modified
therefore resulting in more engine stress

i base non of this on fact lol just what seems logical to me