I haven't tried the straight or SAO curved trigger in a gun that wasn't set up for SAO. I know I got a trigger with much less curvature than the stock one and used it in mine until I converted to SAO. You can do pretty much anything you need to do with a 75B with various parts from CGW and CZCustom.
Yes, if you aren't dead set on SAO, then the P-09 with the decocker is excellent for DA/SA. That is the way I have both of mine set up. I shot SIG P-226 DA/SA guns for several years in IDPA so I am perfectly comfortable with a DA first shot, from a draw. If you aren't set on SAO, then the choice between a 75 and a P-09 is tough. I personally think the P series guns are tighter and more accurate than the average 75, but I don't have a large sample to make any meaningful conclusion. I CAN say that the four P series guns I have shot have been excellent, and that my two P-09's are as good as anything available mechanically. I would pick the model that feels "right" to you. I obviously like the P-09, but the grips were too narrow and blockish the way it comes from the factory and I had to use grip tape and/or JB-Weld to reshape the grip...to get it closer to the feel of a 75.
What I am hoping with the 97"E" is to have the perfect grip shape and trigger reach (for me) of the 75, with the fit and accuracy of the P-09. David has told me that that is not a problem for him to achieve. Video soon.
All said, I wouldn't agonize too much over your choice. Pick the one that feels best, fix the trigger and sights so you can shoot it, and ... shoot it. My bullseye season ended a few weeks ago, and I pulled out my SIG's and Ruger 22/45 and even a Kahr and a GP100 revolver and shot them all. They all shoot great, and I can shoot every single one of them better than I could a year ago, because my trigger finger and eyes and mind work together better now. I could shoot the SIG and the Ruger in bullseye instead of the P-09 and the Kadet if I had to and do pretty close to how I'm doing now. I just like the P-09 and the Kadet a little better. They both surprise me and they are definitely unique on the firing line. They surprise my competitors plenty, believe me, and that is half the fun of showing up with the unusual guns instead of 1911's. Most have never seen a CZ-97. 2015 will be fun.
Heck, I've never seen or shot a 97! David says they are shooters, and I wanted a non-1911 .45, so I placed my order. Not much agony here.
Joe