Added in front squats to my program, my legs are officially jellified now. Did my normal back squats, finishing w/ 6 x 230lbs - then stripped the plates down to 155lbs and pushed out 3 x 8 clean grip front squats. Why? Because I just felt like it.
I don't feel like walking up any stairs anytime soon, thats for damn sure.
As for the SLDL/stiff leg DL thing, I think Exrx has a couple of examples where the movement is done so that the lower back works dynamically (flexes through full ROM, not just isometric stabilization). I've always regarded those variations of the DL as hamstring exercises, so I don't really know whether they hit the lower back any harder. If you're looking for that nice lat taper/definition... I'm afraid it's just a matter of dropping the bodyfat.
Being men, we do have that slight inconvenience that the lower back seems to be about the very last place the fat comes off from (due to the beta-2 receptors or something?). Stubborn fat is stubborn.