I just booked a r/t to CPT myself the same time. I like to venture on other airlines that I have not experienced, but ended up doing an overnight in LHR as a friend is there for work the same time, so my routing is IAH-LHR-JNB-CPT / CPT-JNB-FRA-IAH.

I was entertaining the idea of moving through IST and was even considering ET out of IAD. Also, being in IAH, a lot of routings for GRU was given and thought about day tripping around with the lengthy layover.