When it comes to boots you really need to wear what fits your foot the best. Should be snug but not too tight. If they are too narrow or too tight on your toes, your toes will go numb from the blood flow restriction. Too loose and they will fill with water. For example, Xcel is great stuff, but the boots don't fit my feet well so I can't use them. Best to try on a bunch of different brands till you find what feel most comfortable.
how warm are the xcell 5mm boots? how durable are they? i used 7mm ripcurl fbomb boots last winter. they were super warm, but the neoprene under the balls of both feet wore down to nothing by the end of the winter. the fbomb gloves were super warm, too, but wore through the fingertips (from grabbing the rail at the end of each ride). warm is great, but stuff's gotta last, too.
ive worn the same pair of xcel 5mm split toe booties for the last 3 winters, and got rid of the 7 mm round toes. Rough guess 100+ sessions in those things so far.
They arent as warm as the Xcel 7mm round toes but they feel SO much better. When the air and water are both below 40 the 5mm. split toes start to get cold after an hour or so but its worth it to me to have that better feel.
a lot of it has to do with your wetsuit...remember if your core starts getting cold, the body shuts down blood flow to the extremities so a less than ample wetsuit can cause cold feet and hands. at least thats what ive heard.