Be careful of the Walthers/Shinohara line of curved turnouts. I found out the hard way, unless they have since been modified, that their two radii are not as advertised. The two with which I have experience, now ten years ago, were their curved #7.5 and their #8. Neither turnout was usable once I had them in my hand and learned that I was misled. I had to cut all the webbing under the rails so that I could widen the two routes sufficiently that they would work.
The 7.5 was advertised as 28"/24", but the inner route was closer to 21". The #8 was supposed to be 32/28, but the inner was closer to 25". This ended up discussed on the modelrailroader forum, and others learned that theirs, too, were as I had found. Now, all of us who were affected dutifully announce our experience whenever the topic of curved HO turnouts comes up from someone interested in acquiring them.
Only curved turnouts, or the Peco Code 100 English variety (non-Streamline), have truly curved routes through the frogs. N. American style, Atlas and Streamline Electro and Insulfrog Pecos, and the Micro Engineering, as examples, have a straight route through the frog and beyond, even if the closure rails and points rails are curved. Otherwise, if you have to use N. American style, you must concern yourself with the 'substitution radius', details of which you can find on the NMRA site.
It seems to me that Peco must make set track elements that would conform to their curved turnouts, but otherwise, you'll have to get close. If you are within 2" of radius between your flex/set track curves and a curved turnout, it won't make much difference either visually or practically as you connect them. With variances greater than about 3", it will be noticeable and you'll notice a slight jerk in yaw as the rolling stock moves across the joint. Maybe. Viewed from the side, eyes low to the surface, no.