Due to a question in a forum asking the main differences between Code 55 and Code 80 track, and more exactly how is Peco Code 55 track, I did some photos of both types of tracks that you can see in this post.
I have them installed in my layout and mixed without problems. Code 80 is used only in a hidden yard and Peco code 50 is for all the rest. Nowadays I would use only Peco code 55, but when I started to lay tracks I didn't know there was a more realistic one and I had some Minitrix switches to use. Now all those Minitrix switches and point motors are giving me lots of headaches and problems, but it's too late to change them.
First, here you can see the differences between both tracks. Peco is in front and you can appreciate how rails and sleepers are smaller and more prototypical.
There is a surprise when you face one rail with the other, both have the same height. But if you look closer to it, Peco code 55 sleepers are lifted from the floor. Peco inserts a part of the rail in sleepers and that's how they build a more prototypical track but with the same resistance and consistency.
Leveling the sleepers with the floor you see the difference in height:
Answering the question if both tracks can be mixed, here is the answer. There is no problem and you don't have to adjust nor sand rails if you use Code 80 joiners. Code 55 joiners won't fit in Code 80 rails.
Another good point for Peco code 55 flex track is that it can be bent and it keeps the form. That helps a lot to plan track laying and cuts in rails.
And last but not least, the quality and realism of switches is far away from those Minitrix I started using:
Flex track is also produced with concrete sleepers, but it's not the case of switches. Switches are sold just with wooden sleepers, I hope they plan to have them also in concrete.