Me & wisdom in the same sentence is an oxymoron

Don't worry too much. That exhaust should give you all the enhancement you need (remember, this bike doesn't need much help) run it till it rots & it may never rot. It should be fine. A new tune will do the most for you - Thanks HansO!
With all things considered, you are not even going to Notice the tiny amount of mph that might possibly be lost with the flex pipe (if there even actually is any). That's just splitting hairs. Sleep well with your choice - it will be fine