Carry on size enforcement

I should add, if I DO need to buy a new bag, any recommendations for a roller version? No, I am not doing back pack carry on. I have limits. ;)

What airline will you be flying? British Airways has a slightly larger allowance for cabin baggage--56 cm which is equivalent to 22", while many other European airlines only allow 55 cm.

Depends on the airline. They post their limits/rules on their websites, so look there.

Do you know what airline you will be using? Any inter-EU flights, or just US-Europe then Europe-US.?

Lufthansa on the way there and back and Air France Berlin to Paris.

Lufthansa states carry-on is 8 kg limit -- that's the part that would stymie me.

All I can say about Lufthansa is we have never been asked to size our bags on our many flights. We use a pair of the Rick Steves convertibles and they are always on our backs at every relevant moment. The closest we ever came to an issue was on a crowded connection from Lufthansa to Croatian Air last fall in Frankfurt, the Croatian Air gate attendant tried to make my wife relinquish her pack. Seems she is only 5'1", so this bag on her back looked much larger than the same bag on my back, and clearly must have been oversized!. They backed off when we protested, and of course these fit into the bins on the Airbus 320 without any issue. Now these are soft packs, so if the sizer is involved there will be no issue, unlike hard, rolling bags with wheels. We also make certain before we start out that we are not exceeding their weight limits. We've actually had no issue with these anywhere, and that includes EasyJet, Ryanair and Norwegian.

A person's head could explode from all the considerations! ;) Hard-side vs. soft-side. 0-4 wheels? Size? I'm temtpted to wear all my clothes on the plane and have done with it. I'm now torn between checking the 22" (in which case I'll probably need to get a cheap bag to bring goodies home in) OR half-packing the 25". Just kinda didn't want to drag that thing on the train/metro this time...

If you decide to go with a smaller European sized carry on, we've had good luck using the RS rolling bag. A smaller bag should help you stay under the weight limit. A number of years ago Lufthansa had a lady in the gate area in Atlanta that would walk around, eyeball the bags, and occasionally lift one up. Some she just put back down and some she checked. Must have had an educated / calibrated arm.

We often go carry on to Europe.. but I usually end up using a cheap cloth bag as my carry on bag on way home( loaded with shopping and things I dont want to lose) and check suitcase on way home ( its just filled with dirty clothes by then and losing it would not be end of the world)

Well, after talking to my daughter who hates dealing with getting a bag into an overhead bin, etc., we'll most likely get 22' bags and check it. we'll have to deal with waiting for our bags, but at least they'll be light and more manageable. And then we'll be able to bring a cheap carry on for the way home.

Yes, they really do look at size and weight. If you are a gambler, then go for it, but be prepared to pay or have your bag checked at the gate.

the more full the flight the more scrutiny period

Yeah, that's just not stress I need. We'll be checking our bags. :)

Glad you are checking it, good choice.
I fly Lufthansa to Munich a few times a year from SFO. The agents always make the rounds of the boarding area tagging the carryons. If you are over the limit ,in number or size ,they make you check it.
They do a second check as you are boarding.

Make sure you carry on what you will need for a few days if your bags go astray. We’ve had that happen twice and never check bags outbound as a result. On the return we will as we don’t care as much.

They will more often get you on weight vs. Size. I was in line once and the gate agent singled me out of a large line, and I was one kilo over the maximum weight. The others in line were more heavy packed. I just opened my wife's bag and offloaded 2 lbs. Into her carryon.
I just ask that everyone be measured the same. We were on a flight last Spring returning from Oslo, and the gate agent didn't start measuring until the plane was 3/4 full. Whe we boarded the Boeing 787 and there were plenty of compartments empty. I had to pay $50 for my 21 inch swivel bag to be checked.
I just measured my 21 inch TravelPro soft sided bag with swivels. The bag is 20 inches tall and the handle folds down to 1 inch thick. But the swivel wheels are 2 3/4 inches tall--so I am slightly above airline standards of 21.6 inchs.
It all gets down to what kind of mood the gate agent is in. Usually my 21" bag will pass. But sometimes out come the tape measure. I call it maximizing profits.

Since you are going to check your main bags, consider this. Pack half your stuff in your daughter's bag and vice versa. That way if one of the checked bags takes it's own vacation (and it does happen) each of you will have at least half your stuff in addition to what each of you has in your own smaller "personal bag".