I am the youngest of a family of six and was in charge of the laundry growing up. My sisters tossed stuff in the laundry instead of hanging them up.It was easier to cleanup their mess by tossing it into the laundry basket.
You have young children but I bet they will do this too.

I just installed a LG 4.7 yesterday . There is no center agitator . I will wonder about balance issues whenI toss in the comforter. The load of towels did come out well wrung out/spun out.
I don't think bigger is better.
The key to washing clothes is enough water to agitate the clothes and enough soap to wash them. I have never used a full cup of detergent in the washer. I add about a half of what they recommend.

The difference in drum sizes was a three hundred dollar difference. The difference in drum capacity was the not deal breaker but cost to run the unit and washing options. I did not buy the steam option. I never used it on my three other washers( we move frequently)
I don't know the difference in drum size capacity . HOw many more things can you add in a 4.5 vs a 5.0 should be answered by the salesman.
We tend to overstuff the washers anyhow so bigger does not mean it will be better.

I removed a perfectly working LG steam washer because the unit was a front loader. The entire second floor of our new home shook . Making smaller wash loads did not cut down on the shaking.

Sorry that I didn't really answer your question .
I look at it as what will work . A bigger unit that has the same mechanics may break due to our tendency to over load washers.

Bigger is not always better for large amounts of laundry. Larger capacity means higher g-force loads on every moving part. It hasn't been well demonstrated the new washers are built to withstand the additional wear and tear over time. People are now considering an eight year old washer ready for replacement. That's ridiculous.

I went the other direction toward a smaller, quicker machine. A typical wash cycle is 35 minutes and even with a modest size tub, I can power through a large amount of laundry on a Sunday afternoon.

I just got the LG Mega-Capacity pair, and I love them. I am still trying to get accustomed to how little water it uses. It washes and rinses very well. I just did 3 loads last weekend and I was very impressed. It holds alot of clothes and washes and dries them fast.

The one thing I am very impressed with is the time each load takes. I had the LG topload pair and it would take about 1.5 hours for each load. With the LG 5.1 washer, it only takes about 55 minutes per load. I can't recommend them enough.

Your current 4.3 cf washer may in fact be a 3.6 or 3.7 - did you check the specific model? LG used to give their IEC capacity in all of their marketing materials until a couple of years ago when they switched to DOE. This may also be the reason why your sales person is giving you different numbers. So make sure you know whether it's IEC or DOE on both the current washer and the new washer so that you can compare apples to apples.

I just installed a 5.1 LG front loader with the matching 9 CF gas dryer .... both with steam......I love them......HUGE capacity.......

This is so enlightening! Forgive my newbie question, but what do IEC and DOE stand for? My current LG washer is WM0642HW. I'm sure it has to be around 5 years old or so. The way they market capacity can be so misleading!

Here is a link to your washer info. The LG website lists it as 4.0 or 4.2 cf IEC. So it's probably 3.5 or 3.6 cf DOE. Which means that the new washers you are considering at 4.3 or 5.1 cf DOE are significantly larger.

Here is a link that might be useful: LG Washer

You guys are great! Thank you!