I've only done shrooms 3 or 4 times but each time I tried the high is always "different" (and yet, so the same).I've done acid about 30 times. And everytime I take acid (even off the same sheet) the high is "different" yet the same.
I think it's just the nature of the psychedelic experience itself that guarantess a different "type of trip" each time.
As for mixing varieties of shrooms. It's fine.