I haven't rented for that race but my rental experiences for other races have been great.  The bike shop should be able to tell you what kind of bikes they have available and they should be able to fit you to a frame for your size.  I'm surprised that they will only accept reservations 1 week out.  Most of my friends have shipped their bikes for races and I haven't heard any horror stories yet, but I'm sure they are out there.  I think renting is more economical if you're not particular about having your bike.  You can only make so many tweeks with your bike tool so it may not be as comfy or fit as well but for a short race a rental is less stressful for me.  Someone once told me that its not the bike that matters, its the motor.