Hi Frankie - 

Great question!  There are different industry theories and stories regarding materials used and their affects on feel or performance. The affects of 1025E on club head performance and feel are negligible.  For one piece forgings, it is the structure of the head that driver differences in feel/performance not the material.  

1025E claims to have smaller concentrations of phosphorous and sulfur.  According to the AISI standard for 1025 there can only be up to a max (% weight) of .04% P and .05% S for it to still qualify as standard 1025.  A tighter control of P and S content does not yield a drastically different material, in fact, by AISI standards, it is still 1025.  Typical 1025 compositions have less than the maximums. 

Hope this helps...