We had a hot day (33C/92F) and I tried this on the C230. Evap temp was a constant 4C/40F and the air out of the center vent (Dad's super accurate digital thermometer) was 6C/43F.
So, on the C230, it seems that a close to 50F drop is possible. I think that all of the late model MB's would have that preformance, and possibly less on some older cars. I would think that a 40F drop would be a minimum standard. BTW, our Subaru managed a 50F drop, too.
1998 C230 "Black Betty"