I saw you wanted to go with CO2/Small Backup Pump - that's cool. I prefer the pump, but as long as you actually know how to use CO2 either will work.

But the "group ride" thing - I've never seen this be an actual real life thing. I read claims about it on the internet, but it's seemed like one of the "point that has no merit" things to me.

Because there's only 2 groups that I ride with:

1. Fast Riders. It doesn't matter how long inflating my tire takes, because they don't stop and once I'm stopped it's impossible to catch up to the group. I could simply stop my bike, get off, and get back on again immediately, and I wouldn't be able to catch up (they go faster in a group than I can go by myself because of drafting).

2. Considerate Riders. It doesn't matter how long inflating my tire takes, because it's marginal compared to the overall time. It takes a couple of minutes to fix a flat, minimum, and that's it's things go ideally. You have to find the flat, usually have to take the whole wheel and tire off (supposedly you can sometimes work the tube out from under the tire without removing the tire, but I've never had a time where this actually worked), patch the tube or put on a new tube, put the tire back on, put the wheel back on, and inflate the tire. It's at least 3 minutes, often more like 10 minutes. The time difference between an ok pump and CO2 is about 30 seconds. 30 seconds out of 3 minutes isn't a huge deal, 30 seconds out of 10 minutes is unnoticeable.

Definitely do whatever you think you'll be the happiest, but I've never seen a group ride flat situation where the time difference mattered.