Thank you Mike and nrr. We decided to "risk it", and go for the early train. I think we will attempt a Cab, though intend to leave early enough to walk if necessary. Luggage is limited, but we'll all have a small roller bag. Regarding Mike's "what if someone in your group can't get going fast enough?" the person in our group I would be most worried about is me, and I won't let that happen. ;-]
Part of the reason for leaving early is cost, but also it is getting to spend more time at our destination, as that is already limited. We'll have plenty of time to sleep on the train.
The train is a commuter train, without seat reservations to Lyon part dieu. Tickets are paper and have already been mailed. It says to arrive 15 minutes early for that. It will be the only commuter train on our trip, is there anything else to look for or be aware of?
When we arrive we'll scope out the plan for a quick and painless departure, any advise for making this as painless as possible would be appreciated (where to look for our train, etc.)