fjrsochs- Welcome! I actually was -THIS- close to purchasing an FJR in 2007, even went home to get my checkbook to write a down payment. That was the same day the 2007 "altitude sickness" problem really hit the forum board (eventual recall took care of that problem), and it stopped me dead in my tracks on the purchase. A week later I was perched atop my new 2007 DL650. 4 years and 27,000 happy miles later, I traded the VStrom for my new left-over 2010 FJR (bought May 2011). But more FJR in a minute.
Handling issues with the VStrom- "luggage acting like sails", I wore 4 different 3-piece set of luggage on mine. For the first 2 seasons I alternated between 30 liter and 40 liter Hepco Becker side cases (huge outer dimensions, they were double wall boxes so bigger than equiv. storage volume Givi boxes) that were left over from my Moto Guzzi before the VStrom. For the last 2 seasons, I ran with both large and small Pelican cases, the top loading 1440 and 1430 Pelicans- well documented on the Stromtrooper owner's forum. And always with the Givi E45 top box. The thing that makes the VStroms rock solid is an aftermarket fork brace. Fork braces, by my observation, aren't as necessary for the FJR (I could be wrong), but a good fork brace on the VStrom will give you a rock solid platform keeping the two fork legs in harmony with each other when wind or road bumps try to mess with your handling. 2-lane highway and big trucks flying by? You won't even notice that truck whizzing by you. Moderate side winds/gusts are pretty much a thing of the past, but strong gusts can toss around any bike. I used the KB Fork Brace bought from Murph's Kits. But I digress, this isn't a VStrom discussion, now is it?
Back to the FJR- I've got the biggie Givi 55 liter top box others have mentioned, it's mounted all the time. Great box! I can stash my Aerostich Darien jacket and pants and a fleece sweater in that 55 liter box without a problem, and it'll hold a week's worth of laundry if you need it for that. My factory side cases are also always mounted, and they will hold my XL Shoei Multitec helmet just fine. I'm not a triple-digit-speeds rider, but at those times where I'm droning along on the interstate at a... spirited clip, I notice nothing adverse from the luggage at all.
But I do miss the top loading feature of my old Pelican side cases compared with side loading cases of any brand. Given my drothers, if Yammy hired me to consult on the next generation FJR, I'd spec a new side case design with a top load feature. Givi has a top load aftermarket case, but it's only 21 liters (E21 Cruiser). Their E41 Keyless Monokey case may be partially top loading, but I think the main "door" is a side load door. I hate having stuff tumble out when I open that side case, top loaders are so much better,
in my opinion.
All Givi cases that are either side case only (panier) or side/top mount boxes. Man, the E45 used in side case mountings would be HUGE!
https://www.giviusa.com/Side-hardbags/Monokey-Lateral/
I was just checking the Givi website for FJR fitment. As others suggested, I'd get the Givi top case rack for sure, and not depend on the factory top case rack. I also looked for side racks
https://www.giviusa.com/Fitment-kits/ and didn't see anything specific for any brand of bike, but in the "My Motorcycle" section showing FJR specific products, there was an image with an FJR wearing Givi side cases, but no side racks identified. Might have to call Givi and ask which side racks would be needed to hang Givi Monokey boxes from the sides of your bike, but my guess is they'll have something from their PL or PLX series, or maybe the Wingrack series, for their cases. (Givi Monokey boxes are for motorcycles, Monobox boxes are lighter duty meant for scooters.) I don't recall the size of the FJR side cases, but Givi can provide bigger ones (the utilitarian E36 and E45, for example). And I think the more uniform shape/rectangular shape of the Givi cases is more useful to storage than the sculpted, 6-sided, aerodynamic shape of the factory Yammy cases. Some OEM cases are so over-designed in their shape that the interior volume shape starts to work against you in the sorts of stuff you'd actually want to put in the cases. But they look good, right? Form over function... not my philosophy, but I'm not selling sleek looking motorcycles, either.
That said, you'll love that FJR. Get it tweaked the way you need it to fit your body, load 'er up, and hit the road for miles of mental therapy!