I usually ride with just the big top box. When I washed/waxed the bike this weekend, I took off the top box (of course). Afterwards, I put on the side cases for a change. Commuting to/from work today I swear it felt like any wind was grabbing cases more than I felt with the top box.

Anyone else experience that? Or am I becoming more demented?

I won't try to address the dementia question.

I do almost all of my local riding with the big 49 liter top case attached and the side cases removed. The top case is so large and convenient, it is hard to go anywhere without it. In addition, leaving the side cases off gives me additional wiggle room and confidence when I split lanes, which is allowed here in California.

That said, I hate the top case. I hate how it upsets the natural balance of the bike - it is so high and to the rear. I can handle it just fine while cornering, but I don't like how it pulls as you lean into a turn, especially when it is full. I don't like the way that it catches the wind, especially side winds where its high position levers the bike into leans. I don't like the way it looks. I am a practical person, so I leave it on most of the time, especially around town.

In contrast, the side cases sit relatively low and closer to the center of gravity compared with the top case. They do catch side winds, but they don't have as much leverage to lean the bike as the top case, so side winds tend to push the bike laterally, rather than lean it.

Given a choice between side cases or top case, I prefer the side cases. Around town, I use the top case. On longer trips, I start with the side cases, and add the top case only if required.