MIDI controller keyboard: latency diff. btwn. USB & MIDI cable connection?

Whatever MIDI keyboard controller (which I'm using at the time for little more than key, duration, and velocity data transmission to soft synths) always has options to connect either with MIDI cables to my UA-25 external sound module or with USB to the PC. Lately, esp. since I sometimes use significant CPU layering synth elements & effects, I've been connecting the keys via MIDI cables to the UA-25 to avoid making yet another USB connection to the PC. 
Back when I didn't know yet latency causing me to hear a delay between pressing a key and hearing it begin had far more to do with optimization, settings, & drivers, I wondered if one or the other physical connection between keys and system made a difference. A guy at the music store insisted, "USB is WAAAYyyy faster than MIDI cable...", which is surely technically true under certain circumstances, but I'm not trying to send Encyclopedia Galactica through my cables, just  notes played with human hands.
I'd swear using the existing connection (& drivers for that matter) of the UA-25 uses slightly less computing power to receive notes than separately plugging the keyboard controller into the PC via USB. Since I have the actually, primary latency causes well under control these days it's not an issue per say, but I'm wondering which the gurus would plug in regarding this common setup, if there's a preferences and isn't just 50/50% either way.
Any thoughts?
Thanks!
-Jeff
P.S.
Another reason I opt currently for ye old MIDI cables to UA-25 instead of additional USB is any time I'm on the fence I'll, if for no other reason, choose the one that doesn't run extra power though my PC; without using USB for the controller keys I use separate power for them, just as I like to use a physical mixer for mic phantom power when I can in lieu of that optionally provided by the UA-25.

It's a musical instrument. Play it the way you hear it.
 
Some synth sounds have a faster attack (sound envelope) when you press the key down too, so you'll hear the sound faster.
 
I don't know the details, but cheap usb cables, old usb plug 1.0, old motherboard in the pc, slow cpu, etc, etc, could be slowing things down. Like usb 3 is out, but if you install a usb 3 card in the pc, most motherboards still can't handle the extra speed.
 
I agree with bitflipper, midi cables were made to handle midi specifically, so you'd think they would be better and faster than a generic usb plug. Time to call the techs at the keyboard company and see what they say.
 
Explaining USB 3.0
http://www.youtube.com/watch?v=C-N_vN_tmA0