I ran 49 Skinks with Poison and 1 Kroxigor the other day. I was playing against Tomb Kings so it may not be the best example, but they held up pretty well (give a little bit of luck).
I put the single Kroxigor in the unit for Ld 7 mainly and run them in horde formation (although they are only a reform away from being 10 ranks deep if I really need some steadfast).
I ran them right up the middle of the field and got charged by a unit of Tomb Guard with a Tomb King. Skinks won that round of combat. Then they got charged in the flank by Necolith Colossus and also charged by a unit of Skeletons. They didn't win that combat, but they were steadfast and held. (I should note that this turn the Skinks has Light of Battle cast on them so they were WS10, which probably makes a big difference .. but that's why I take Lore of Light!)
That was enough time for my Temple Guard to get a rear charge in on that Necolith Colossus. Unfortunately the Temple Guard wiffed on their attacks and didn't kill the thing ... and the skinks were reduced enough that they were no longer steadfast and I lost combat ... but rolled double 1's for the skinks to hold!
This whole time the Skinks had been picking away at the Tomb Guard, killing 5 or 6 of them a turn.
Then a Necrosphinx hit the Skinks in the rear. The Temple Guard killed the Colossus but the Skink Cohort was reduced down to only the Champion who fled (that would be a 450 point Skink running across the table...) but the Temple Guard cleaned up.
All in all, I think the Cohorts did exactly what I wanted them to do. They held up some combat blocks long enough for my Temple Guard to hit them in the side. They needed a little bit of magic (but what in the Lizardmen don't) and a little bit of luck at the end (the double 1's made up for my Stegadon getting overrun after failing a stubborn, rerollable, cold blooded 9)
I'm not sure if 36 Saurus Warriors would have out performed the skinks (they probably would have killed more, but I think the extra 16 wounds in the Cohort unit (for 3 points less than the Saurus unit) let them stick around a little bit longer (at least against the things that didn't care about T4 vs T2 like the monsters and killing blows). Also, the Saurus wouldn't have been able to get far enough ahead of the Temple Guard to block my opponent from charging my Temple Guard. Probably the M6 vs M4 is the biggest tactical consideration to make between Saurus and Cohorts.
For now, I'm going to keep running my 49/1 Skrox unit.