I only use Martyrdom if I'm feeling particularly suicidal at the time - generally it's Steady Aim. M60's have wicked recoil, and with both the grip and Steady Aim, I can manage it quite well. Deep Impact is not all that useful for me, since the M60 can shoot through almost anything anyways (once, with Deep Impact, I shot someone through one of those thick curved steel plates around the silos on Countdown).
For my set, the more open maps are my friend - LMG's don't seem to be that great in close range. Quite lethal at medium-long, though.