I’ve been going back through old posts about tips for century rides and I have learned a lot. I’m starting to form my plan for the supported century ride I am planning to do next month. The longest ride I have completed is 50 miles but I did it really before I was giving any thought to the technical aspects of my riding. I just went out and rode 50 miles. So for the this ride, I’m planning to shoot for .65 -.70 for my power. But one question I had that I hadn’t really seen any thoughts on was RPM’s. For a long ride should I be striving for higher rpms 100+, or a leisurely pace 85-90.?
I’m jut looking to complete the ride, and not trying to win. I live in a mountainous place, so I do a fair amount of climbing every time I go out, but this ride will have more climbing than I have ever attempted in one ride and I am sweating it bad. (I’m not to proud to get off an push. I’ve done it before, but I really want to stay on the bike.)
Whatever feels comfortable, don’t overthink it. 100 seems way too high to me for a ride of relatively low intensity. I would feel like I was spinning artificially high for the sake of it (though 100rpm comes naturally to me if I’m doing VO2 intervals), 80-90 would feel more natural.
I can’t say that I really look at my cadence very much, unless it’s party of the workout instructions. I really wouldn’t worry about a “proper” cadence, except maybe on any long, steep climbs. It’s totally normal to freak-out about about the amount of climbing. Just pace yourself early on and smile when your legs feel like they are going to fall off. 
For this ride you don’t want to be thinking about your cadence at all. This is the perfect time to put into practice all that research that says that self-selected cadence is the most efficient. By all means keep practicing different cadences in training, but your first century should be treated like a goal event, and I would never watch my cadence during a goal event like that. I wouldn’t even have it showing on my head unit - just look at it after the fact if you really want to learn from it.
Hide the cadence and go by feel.
unless you are trying to do a workout, I’d just go out and ride at whatever power and cadence you want. The best things to focus on are eating (and/or drinking carbs), and drinking fluids.
Ride at whatever cadence feels comfortable, don’t have it as a data field to be targeted. It’ll vary naturally throughout your ride anyway.
Unless you’re riding around at like 50 rpm’s I wouldn’t worry about it. Just cruising around, 80-100 is normal. Just ride at what feels comfortable. Unless you feel you have a specific reason to change it, I wouldn’t.
In my mind, you should just stick to whatever feels good. Usually your self-selected cadence varies with speed and terrain. Most riders will prefer a lower cadence at lower speeds, in part due to the lower rotational inertia.
Sounds like you’re way over thinking this. Just go pedal your bike like you always would.
Think about your gearing, don’t overthink the cadence. However, I would suggest having a look at what cadence you held on similar climbs in the past. If you’re doing any long sweet spot intervals on the trainer try and do at least one of them per workout at that cadence.
You have your power plan, just go with that and let your cadence just feel natural for the terrain you encounter. I would put a reminder to eat/drink on my headset before I would worry about it showing me cadence for this ride.