I wouldn't say slow, it's probably the least noticable of all his attributes, but you're bound to look slow when you are putting devastating force behind punches. Besides, who needs handspeed? Timing, precision and ring smarts can counter that and SNV has all those in abundance, so much so that I heard he donated some of his left over technical skills and ring IQ to Floyd Mayweather in exchange for PBF sponsoring an Amur Tiger.