I hope to crit in March '07, for the first time. I've bumped, hooked, been taken down half-wheelin' and been in some close quarters with large groups. I definitely have to practice not being squimish when w/in a foot of others bars on the left and right at speed, where you can't get out of the saddle or even rock the bike w/o hazard.
As to 4.7 watts/kg, I should think simply time trialing ahead would score a win at cat 5, no? I'm a tick below 4 w/kg (including bike) and feel pretty comfy diving into a sub-25mph group. Still, my hope is for safety and I am thinking of just coming around them for short, short, pulls and then, more importantly, gaining confidence as I drift to the back, however tight things are. I expect the culture will be entirely different.
There are plenty of reasons to have a power meter if you aren't going to race. They're really important to the non-racer, IMO. Time trialing and triathlons are becoming a science with them.
Unless you are the second coming of Merckx, very few people will ever time trial off the front of a field in their first race. Sub-25mph will not pull away from anyone except the guys who are just pack fodder in the first place. Also, you never want to drift to the back. It's very hard to move up and you'll more than likely get caught behind or in a crash back there. Everyone and their mother is going to tell you to stay in the top 1/4th of the field, and rightly so. It will be smoother and less dangerous up there. Better, smarter athletes who know how to play the game (relative to the category).