Hello,
There really isn't much difference in taste. I have tested the difference a couple of times at family functions. I never make pies without strawberry rhubarb, but I usually mix the varieties that I grow. On the occasions that I made one with just strawberry rhubarb, it was slightly prefered to the ones with mixed varieties. I don't notice much difference. I always get several requests for rhubarb pie for any parties. Of course if you add strawberries, you mask the rhubarb so it couldn't make a difference. I tried a rhubarb pie with strawberries and there is no comparison. Strawberries are much better left to dip in chocolate or for shortcakes.

Thanks,
Bill