The increased drag due to the increased lift required to turn will always reduce the climb rate/angle. The greater the bank the greater the reduction.
For the 605, page 06-04-18 of the AFM gives you figures for 15 degrees of bank clean and flaps 20, which are 0.30 and 0.38%.
The important thing to remember is that the reason we use half bank following an engine failure is that at V2 with flaps 20 or Vt clean we do not have our normal margins above the stall, so bank should be limited to 15 degrees. Also at high level we use it for the reasons others have given. Luckily the Challenger automatically reverts as we descend or, if you've activated it lower, when you try and commence an approach.