Hi,
We towed an Eriba (Hymer) Triton (MTPLM 1200 kg) with the previous generation C270 CDI Avantgarde automatic for four years.
The 5 cylinder C270 engine produced just a few more bhp and a bit more torque than the current specification C220 170 bhp - and whilst the ratio was slightly better than the 90% ratio of your combination - our experiences both solo and towing were all positive.
And a year or so back, replaced the C with an E-320 CDI, which excels at the same job.
If you are going to buy a C-class, I assume it will be an automatic? The manual is fine, but see if you can live with the parking-brake (which is a non-issue with the automatic)
Regards, Robert