Yippee, my experiment results
OK, I tried your whole wheat banana sandwich bread and it turned out good. As crazy as I am... added sesame seeds seemed to add the crunch.
Then yesterday I used both SD and water roux starter to make my regular SD wheat sandwich loaves. I didn't use a lot of water roux starter, 1/2 of what I'd used in my banana bread, about 50 grams. The rest of the ingredients remained the same as my original recipe. The results... not much difference!
Since I used more flour and more water (the water roux starter) the total volume increased (expected). The flavor was not as strong as my regular SD (probably had to do with the fact that I didn't feed my starter for a week - too busy playing with water roux bread LOL) and I used kefir whey instead of yogurt whey. The only sorta significant difference was rising time. My regular SD dough usually takes about 4 hours to rise 1st, then about 2 hrs for 2nd rise. But my dough yesterday took about 3.5 hours and 1.5 hrs respectively. I am not sure if it had something to do with the fact that our days are getting warmer or the combination of the SD and water roux starter sped up the process.
Next time I will try to use a bit more water roux and a bit less SD starter. Have to wait for a week though. We have three loaves of breads now and I don't want to make any more. That would drive my husband crazy! ;^)