"Whoo Hoo! what a great bike! Now I'll really make it!"
I saw several unusual bikes being used to ride STP: a young couple each had a "market basket bike" with wide-ish tires and front bike basket (full of stuff) and were determined to ride it in two days. Several people were on unicycles bound and determined to make it to Portland. And then there was a large variety of road and mountain bikes, not to mention my good, old 1998 9 speed.
Yes, a good bike can make a difference, but if I bonk it is pretty meaningless. It is important that a person be ready and able with a "good enough" bike, then there are other things that, while maybe not make/break like fueling and hydration are, can make it a "fun ride" or "I'm not doing that again"
As far as "good enough", assumenda nesciunt reprehenderit est mollitia:
Now, the 11 speed Ultegra bike I've tried......