Put together a nice wheat recipe and ferment one batch with Koelsch and another with Trappist yeast. I just did this. They both Fermented well at the same temp. The taste difference was amazing- one being crisp and citrusy, the other more malty with spicey clove like flavors. Both great for summer drinking.
+1.
I would take this further in that I believe doing split batches with several styles and using a traditional strain and a Belgian strain are great combinations. The reason being that you can add simple sugars and spices to the primary easily to "tweak" the Belgian beers. If you are looking for purely yeast differences, then this may not be ideal, but if you are looking for some differences in yeast AND producing a (often very) different beer, then this works great. You only brew once, and you produce two distinct beers.
Some of my favorites are:
Brown Ale (w/American or English yeast) -> Add 1-2 lbs of amber or dark candi syrup after high krausen. This makes a nice Dubbel to BDSA style beer. Also good with mild spices boiled with the candi syrup/sugar.
American Pale -> Add 1-2 lbs sucrose or amber candi syrup after high krausen. This makes a nice Tripel Pale hybrid. Also good with some coriander boiled with the candi syrup.
IPA (American or English yeast) -> Belgian IPA (sugar optional)
Stout -> Belgian Stout
Bock/Doppelbock -> Add 1-2 lbs of amber or dark candi syrup after high krausen. Another nice Dubbel or BDSA.
Wheat -> Witbier (boil a tea with orange peel and coriander, and add to primary)
Note that these won't be quite true to style (e.g. hop varieties), but they make fantastic hybrid beers. And that's the great thing about homebrewing - you get to decide

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