They are both fine.
I sometimes use my 26. You need at least 3 mags, and a mag carrier on your belt which holds 2 of those mags.
One problem with your 27 is if your mags don't hold 10. IDPA is oriented toward 10 round mags. Except for 1911's which I forget but probably 8 round mags is the standard there.
Another drawback is .40 competes against 9mm, whereas the .45 only competes against itself.
Of course, ideally you are really only competing against yourself, increasing your own accuracy, and decreasing your times, no matter what everyone else does. But people generally still want to do better than other people
I'm much better with my 17 than with my 26. Longer sight radius, better grip, less recoil. But I carry my 26 more in the real world. So, should I use IDPA to get more experience with my 26? Or should I use my 17 to try and beat Tom, Jesse, and Barbara?
There is no right answer, but the more often people do IDPA, the more likely they are to get a gun just for it. Thus, I use my 17 much more in IDPA, to try and be the best I can at it (which isn't that good or that serious about it). Still when I go to the line, I want no excuses. If I lose I don't want to blame my gun. I feel my 17 lets me compete to my fullest. A 34 might be a little better, but probably not much for me (enough better if I was really serious), but a 17 has big advantages for me over the 26. Even though I should probably buy a 2nd 26 and only use that in IDPA