I bought the View 71 case with the intention of mounting the GPU vertically - I must say an excellent case with tons of room but as you can't hide the cables a bit more thought needs to go into routing them around the case and making it look tidy.
Issue I had was the damn CPU cooler was just a few mm too big (even with the offset at max), so had to resort to the standard GPU installation.
Can't recall reading anything about loosing fps via the use of riser cable, just need a quality one to ensure the signal is 100%.
I still intend to install the GPU vertical at some point in the future.