They both have the same buckles, straps and laces.
They both have the same wheels, 85A Flying Eagle High Rebound Wheels.
They both have the same ABEC 7 bearings.
They both come in 2 colours, the F6S comes in dark green and red, while the F5S comes in black and black with pink.
Differences
The F6S costs $229 while the F5S costs $189. At these prices, the F5S gives you more bang for your buck. However, if the price of the F5S increases past $200, which has happened in the past, then the F6S provides better value for the money.
The F6S has a studier EGO frame that looks gorgeous, but is more difficult to clean. The F5S has its own unnamed frame.
The F6S has a more comfortable liner than the F5S.
The F6S also has 7 mounting holes, which allow you to adjust the frame position from side to side, and from front to back. The F5S only has 3 mounting holes which only allow you to adjust the frame position from front to back.