first of all, read this. i may be sounding like an ass, but the same things have been covered many times over, and the best tips have even been put into a sticky

as for speed, like the price of an expensive item, if you have to ask...

no seriously, there are 5's who are just on their way of upgrading to a 2, and then there are the 5's who will spend a long time toiling in the 4's. go into the racing sub-forum, look up a few posts (carpediemracing's come to mind), and read. in fact, you may want to read carpedieracing's blog as well, very informative.

the crits will average about 25mph for 30minutes, but that's not the whole pictures. for starters, drafting saves you about 20% in energy consumption. other than that, ask yourself these questions (almost blatantly lifted from CDR's post):
-can you corner (say at 25mph into a 90 degree right turn)? do you know how to cut the apex? do you maintain the same turning radius through your turn? do you find yourself overcooking turns?
-can you ride with people on your left and right, moving up and down
-do you check who's behind you when you move to the left or right? could you do so without swerving your bike?
-do you know how to brake when the person in front of you slows down? do you know how to feather your brake?
-do you find yourself allowing a gap to open when the wheel in front of you accelerate?

if you answer the above honestly and find that these answer may not be ideal, you should not race as that will be a danger to yourself and to others. in my first two crits, i have seen three crashes. two of these were caused by guys who can't corner & slid out because they overcooked the turn. you do not want to be the person crashing out others

with regards to speed, a lot of it has to do with positioning. if you find yourself midpack in a cat 5 race, you'll slow down to 17mph going into corners only having to accelerate back up to 28mph to catch up. you'll waste a lot of energy racing this way, not to mention that the risk of crashes increase when you are cornering with people who may be suspect. jens voigt wasn't spewing nonsense yogism when he said the safest way to win is to arrive by yourself. the fewer the people in front of you, the better, as you can take the safest, fastest line around a corner. now, given that you live in nyc, this won't matter as much as the only true crit around is rockleigh, but it is still quite important as a competent racer should be able to negotiate the turns of harlem hill at 30mph without drifting. CRCA hosts training races. they are highly recommended if you don't have a coach who can guide you