As far as I know Wagner stock two different intercooler's for the 1M & 135i, I guess due to bumper size. If you are running a stock, genuine 1M bumper then I'd say get the 1M intercooler but as for replica bumpers which fit with stock 135i fenders...who knows.
I'd contact Wagner and ask them to make sure, you may even be able to buy a 135i intercooler and trade for a 1M version if it doesn't fit if you explain to them what you are doing.
As for data, I spent a fair bit of time talking to Wagner UK and the figures looked good. Temps were way down on stock and I've no reason to think that the fact it uses stock couplings hold it back at all...that's down to debate though. For a true drop-in intercooler there is no other, ETS requires removal of couplings and installation of additional pipes but it is also a no-trim option and a very good one too.