I almost always race in the big ring during a crit.....but that doesn't mean you cannot spin at high cadence just because you are in the big ring.

My58vw....you said that you cannot spin at a high cadence above 100 comfortably...which is precisely why you should do it in training until you can become very comfortable doing it....refine this skill until it becomes as natural as breathing. Repetition is the mother of skill. It is a skill not a genetic gift...so that means this can be developed. If you are really having a problem with it then I can tell you that this is a handicap to you and that you will become a better road racer when you work to overcome this handicap.
Every training ride should have a predetermined purpose. Try to work on your high cadence spinning perhaps a day or two per week. As your muscles and neuro pathways are developed through this type of training...you are going to become much more economic and effecient. This is going to pay you dividends if you start now. You will see results I guarantee you. As a result of being much more effecient...you will have much more in your tank later in the race. You are going to find the race pace a bit more comfortable and you should find it easier to stay comfortably in the pack when the pace is hot and some of the others are much less comfortable than you. Having more in your tank later in the race will mean the difference between finishing with the group versus getting dropped, between finishing 3rd instead of 18th. Good economy and effecient pedaling technique will shift the energy burden to the most effecient systems. The physiology systems that are most effecient for sprinting should not be accessed and exhausted during the middle and later stages of the race due to poor technique...but should instead be reserved for the finish. But those that have poor economy and effeciency will often do just that....and the energy burden is often placed upon the wrong systems at the wrong times. It is because the muscles and nerves are not properly refined through purposeful and repetitive training. It's like trying to write with your left hand(assuming you are right handed)...but you can get better with work.

I do not consider this a specialized skill...but rather a more basic and fundamental skill. It is part of your foundation as a racer that should not be neglected.