Nissbird - After you do this and realize the consequences, then return it to the 20mm lowering and correct the side stand, you will realize one of two things. You're either in the market for a R1200GS Low suspension, Low seat bike, or you will be spending some more time at the gym to build strength.
I have a 29" inseam, 17.5 stone and typically my bike is well loaded with extra fuel, a gallon of water and a full pannier of tools, etc, plus the other pannier full of clothes. Not quite as heavy as having a pillion. I wear Gaerne G Midland boots and only get my toes or sometimes the ball of my foot down at stops. I also have custom suspension at stock height levels, no lowering there. (Touratech/Ohlins) and a custom Russell Day Long seat. The seat moves me up another 25mm over the stock seat.
Nothing you have described warrants lowering the bike at all. With a 20mm lowering, you're doing something else wrong if that wasn't enough. This is my second Super Ten as well, Gen I in '11 and now a Gen two earlier this year. Neither bike lowered. I did lower by 25mm dogbones and 13mm drop in front for my wife to ride. She did fine with that and is 5'6" and 10 stone. She decided not to buy a Super Ten and got a R1200GSA Low/Low instead. (Twice the bloody cost!) She loves that bike and rides it well, even in Enduro Pro mode which moves the suspension up quite a ways.
You have ignored the first response to being inseam challenged. Get a custom seat! One that gives you a lower height.
Sorry to beat you up M8, but you are heading for an unpleasant situation. We all have the odd drop or tip over. Being able to flat foot when stopped won't help when you have loose pebbles and odd angles, it will still go over. Pillion challenges sometimes mean for extra struggle at stops. I understand that. Extra attention and planning and good communication go a long way to account for this.
You will do what you will do. All I'm saying is that you will regret dropping the bike 40mm. And speak to a proper suspension shop before you order your springs. Dropping the front 40mm with shorter springs is not going to maintain the proper geometry. Not to mention spring rate impact. The bike will have very slow turn in with 40mm shorter springs in front and 40 mm dogbone drop. Which means longer dogbones, but not 40mm longer.
Best of luck and I hope I'm wrong and it's brilliant for you.