As the bigger stronger man, with his skill level and talent, sure I could envision a scenario in which Martinez wins. I don't know that he would win but I could see a way.
I pick the Floyd that fought JMM to outbox Martinez, even at 160 but now, his legs are really gone and he just can't box and move like he used too.
Yes, of course he would beat him. He would not be overwhelmed by Floyd's speed at all, and could press him and beat Floyd on points.
I honestly think that's a mechanical problem with his style 140 and above, and has less to do with his age.
Floyds legs have been greatly diminished and was noticeable even in the mosley fight, but has since gotten worse. However floyd still has heaping fistfuls of alternative talents to fall back on. At this point he can take a few cake wake fights and maybe a pac bout and sail off into to the sunset. Martinez needs to seal his legacy at 160 and maybe meet Ward or another top SMW, and leave the lighter guys alone.
Watch the JMM fight. What's the most telling punch Floyd used? The leaping left hook. His legs were much more springy and explosive in that fight. Then watch the Mosley, Ortiz and Cotto fights. The leaping left hooks start to diminish and i don't think he even threw one leaping left hook against Cotto. That and the lead right hand was his bread and butter. And he's been fighting mostly flat footed since those fights. I seriously doubt by choice. He is right at the age when you really start to lose the natural spring in your legs.
He has the style to get into a "boxing" match with Floyd. His style doesn't rely on imposing his size and strength either I see Floyd returning fire with his own jab whenever Sexy jabs then puts it into his holster at the waist. Floyd can also catch him with all kinds of rights to the pit. Sergio's hands down style isn't going to be doing him any favors against Floyd's lead rights.