PSE&G specs (NJ) are: 1/4" Galv wire and a 30 degree min. angle; "securely fastened to anchored studing". Also, RGC mast must be attached to structure (house) with 1/2" machine through bolts thru wall studs. min of 2 straps, each 1000lbs horiz pull. Minimum conduit 2" max 3".
From PSE&G Green Book, 2005 Edition. I have heard rumors that they now want 2-1/2" RGC as a min.
John, I did a service not too long ago that the other "mechanic" claimed "didn't need no stinking guy wire." He also only used (1) 2" thinwall strap! Thinwall! Machine screw bolts? LOL! Sheetrock screws! He was a know it all so who was I to tell him otherwise? Amazingly, it passed inspection. I wired the panel and did the grounding.