The X Air Standard has a 9.8 metre wingspan. The F has a wingspan of 10.05 metres, so the F has a slightly higher wingspan.
Furthermore, the X Air Standard stalls at 26 knots (30 mph) while the F stalls at 27 knots (31 mph) no flaps and 23 knots (27 mph) with flaps.
The cruise speeds are also different: 56 knots (65 mph) for the Standard and 59 knots (68 mph) for the X Air F. <---these are for the Rotax 582.
There doesn't seem to be that much difference really.