Based on my experience with the Strom, at that weight you are going to need most of the "preload" (I hate that word...) capability to get near the appropriate sag ie "not too much sag
I think two of the main reasons for a hard ride are too much sag, in other words suspension compressed too much, and insufficient rebound damping - up to point.
In the first case, when the suspension is over compressed, the "steady state" position (where it is unless responding to a bump) is deeper into the rising rate area of the linkage. This effectively increases the spring rate (it's designed that way). I don't think the V-Strom is as sensitive as some other bikes to this effect (in other words the rising rate is gentle), but in principle it's nonetheless very important to have the correct sag on any bike, particularly one with a variable rate linkage to the shock.
Secondly, if the rebound damping is insufficient, the stored energy absorbed by the spring after a bump is fed back into the bike too suddenly, giving that "hit up the arse" feeling a few milliseconds after the bump. This needs to be tweaked out by increasing rebound damping, but not too much though, because over quickly repetive bumps too much rebound damping can cause "pack down" of the suspension, then you're back to the first problem. Keep in mind rebound damping can go off surprisingly quickly from new, so will have to be increased from stock as the bike ages.
Maybe ignore the naysayers who will post after me (
) and try this experiment. As I said, I'm thinking that for a stock bike, you will need most of the reload adjustment for your payload. Don't bother with the finicky business of measuring the actual sag, just wind it up (carefully, gently and not forced) up to the maximum, then back it off one ring on the shock. This will NOT make your suspension "harder", in fact the contrary will occur. Then add 1/2 - 3/4 a turn in on the rebound damping from stock. I'd bet a jelly bean (colour of your choice) that puts you in a good ballpark for the sag. Go for a ride and see if there is any improvement. Those settings I've suggested are large enough to hopefully notice a change, (better or worse your call) but still allow scope to adjust each way. Fine tune to taste, else if you feel the need, go thru the process of setting sag by measurement...
Personally, I gave up on measurement a long time ago, it can be tedious and has a measurement error risk. As long as when I sit on the bike the suspension is compressed approximately one third ( or slightly less) from topped out I use that as a start point for fine tune by feel. My Strom done that way, and I've fixed up a couple of others by that method too, 'cos I couldn't get them off mine after swapping bikes! In both those cases the suspension was wound down to be lowered for better seat height, I get why people want that on the Strom, I just live with what I get from an appropriately adjusted back end...
Hope that helps.