While I am NOT an expert on x-wings, or casting/recasting parts, I'll tell you what I know about the GR x-wing.
I have heard a couple of people acuse GR of being a recast, but I dont believe it is.
For reference, I currently own:
1)a built Salzo V3.1
2) an Icons x-wing
3) 2 Captain Carboard x-wing kits, one of which I am building now. One is a new casting from Scott, the other several years old.
4) an unbuilt Salzo V4
A year or two ago, I received the Icons x-wing in horrible shape. Pretty beat up, as well as the typical wing warpage. I contacted Ray Perez of GR, and asked him if he would cast a complete set of s-foils for me. I wanted everything, essentially, but the laser cannons, and the fuselage to use to restore the Icons ship. Ray made the parts, and I restored my x-wing, and it now is a nice piece in my collection.
Since then, I have had the opportunity to aquire several other x-wings, mentioned above.
I have compared parts I received from GR directly with the x-wing kits I have now. Dimensions are similar, but not the same, between the two Salzo models and the GR. Even my untrained eye can see casting flaws in different places between the Salzo and GR. The Saturn cans, and the Phantom engines are an example here. I see different flaws in different places between the models. I know very little about resin casting, but I would think I that if one directly copied parts from someone else, the same flaws would show up between parts.
There are several differences in construction technique too. Similar, (as I imagine one would expect with 2 models of the same subject), but NOT the same.
There are several detail differences too. One example is (I don't know the correct term for this part, so bear with me) the parts embedded in the trailing edge of the wings. Salzo uses a separately molded piece, and a brass rod to fill the recess. The GR wing, the assembly is molded into the recess. The detail difference is very apparent. The chips are different, as are the details on the inside of the wings. Similar, but different.
There is virtually no similarity between the CC and the GR wings...not even close. They are completely different dimentially. Saturn cans and F4 engines are the same, but I see flaws in different places between them. Hell, there are casting differences between the 2 CC models!
I cannot speak for the GR fuselage, but I do understand it to be, from several sources, based on the Maxi Brute fuselage. I do not own either one to compare.
People can say what they want about the GR x-wing, but my direct comparison of the parts I have convince me that it is NOT a recast.