I have a similar problem with my LG 4120 (A111 firmware).
Fortunately, I don't have much 4x media left. What I do have is either Verbatim (MCC01RG20) or Traxdata (RitekG04), and neither will overspeed.
However, my NEC 3500 will burn both these at 12x (with Quickee Beta 3 firmware) - although the Verbatim is much the better burn (and done in 6.50 mins).
I don't buy 4x discs anymore, as the (good) 8x media is about the same price and will burn at 16x.