My feeling is that Federer often struggles against Simon. Look at these scores.
2014 Shanghai Masters F Hard Roger Federer Gilles Simon 7-6(6) 7-6(2)
2013 French Open - Roland Garros R16 Clay Roger Federer Gilles Simon 6-1 4-6 2-6 6-2 6-3
2013 Rome Masters R16 Clay Roger Federer Gilles Simon 6-1 6-2
2011 Miami Masters QF Hard Roger Federer Gilles Simon 3-0 Retired
2011 Australian Open R64 Hard Roger Federer Gilles Simon 6-2 6-3 4-6 4-6 6-3
2008 Tennis Masters Cup 11 Hard Gilles Simon Roger Federer 4-6 6-4 6-3
2008 Canada R32 Hard Gilles Simon Roger Federer 2-6 7-5 6-4
Simon gave Berdych a hammering. I pick Federer to win in 5 sets.
2014 Shanghai Masters F Hard Roger Federer Gilles Simon 7-6(6) 7-6(2)
2013 French Open - Roland Garros R16 Clay Roger Federer Gilles Simon 6-1 4-6 2-6 6-2 6-3
2013 Rome Masters R16 Clay Roger Federer Gilles Simon 6-1 6-2
2011 Miami Masters QF Hard Roger Federer Gilles Simon 3-0 Retired
2011 Australian Open R64 Hard Roger Federer Gilles Simon 6-2 6-3 4-6 4-6 6-3
2008 Tennis Masters Cup 11 Hard Gilles Simon Roger Federer 4-6 6-4 6-3
2008 Canada R32 Hard Gilles Simon Roger Federer 2-6 7-5 6-4
Simon gave Berdych a hammering. I pick Federer to win in 5 sets.