speakers

hello all,  i'm currently in the market for a new amp to accompany my vibroverb. I've found the one i want, and am just about ready to purchase. The head is an 18 watt ceriatone, and i'm going to be using a 2 12 cab.  joe and everyone else seems to like the EV speakers, so i'm exploring options there. i've never really experimented with higher watt rated speakers vs. lower watt rated ones. how do i justify the right speaker to match the head. Will a higher rated speaker give a darker tone?, and lower a brighter tone? I remember joe saying EV's can take plenty of abuse.

here is a clip that is pretty close to what i'm trying to achieve:

http://www.youtube.com/watch?v=shmsSb3Usoo

and feedback or advice about how to match speakers for different tones is appreciated. 

thanks,
Brian, central IL