I would look over the RS tour rules and see if it says anything about baggage size. I bet it doesn't.
Baggage size varies by person. How could it not? I went to a few of these How To Pack Smartly presentations, some by an RS staff person. Invariably, they are done by a 5'5" 124 pound female whose clothing and shoes are at least 35% lighter and smaller than that of 6 foot 180 pound man. Of course, the man needs more room.
The presenter will then argue that as a female she need to bring more stuff. Maybe so, but does it make up for the fact that she can squeeze three pair of shoes in the space the man needs for two pairs.? That his clothing from underwear to jackets is far bigger and bulkier? Of course, not.
Bring the size suitcase you need just make certain you can tote it about on your own. Nothing is worse than seeing some 5"2" gal enlisting an other lady's hubby to tote her bags up three flights of stairs, while the guy's wife is managing to handle her own luggage without him. I've seen this. The ladies get more upset about it than the men.
I travel with one carry on size suitcase, and one day bag that hangs off the handle of the suitcase. And I am that 6 foot guy with big shoes for my big feet, and bulky jackets, sweaters, etc. all the way to my socks.
Yes, it's tight. And I manage just fine.