Haven't driven the 140 sorry, lots of threads on FR mpg, you can get 50mpg+ but realistically an average of 43-45 ish.
Biggest difference between the 2 is the DPF on the FR so read up on that to
help you make a decision.
The diesel FR is only a fraction slower than the petrol FR and certainly doesn't drive like a diesel!
I would imagine the FR is a lot quicker as some are 190+bhp standard but you could always get a 140 and remap it, it wouldn't be much slower then!
I'm sure you will get loads more replies, good luck making your choice!