I'm not implying you are a jerk, I don't know who you are or what you do, no more than you know that about me.
I think playing 'fast and loose' for the sake of vanity, as so many would like to do, often needs to be questioned. I think you have in the past posted images of your T4 with both sets of wheels, the flat fives as you call them are not to be questioned.
The big problem comes when people think any old Audi wheel will do; or worse still, they unknowingly purchase 'lookie likies' and then they do collapse. I am sure there are more than dozens running the same or alternative Audi wheels, but load rating recommendations are there for a reason; whatever people may think.
The front end of heavier T4's carries a lot of weight, you then add to the driver, one or even two passengers, and maybe an additional battery under the bonnet; the forces on those wheels can be huge. I realise a lot of assumptions may be worst case scenario, but who wants to be involved in one of those. We also have roundabouts here, again the wheels are put under additional stress. You could go through life trouble free, then again you may not.
Look at all the T4's for sale in Germany for example, very very few of them are full of DIY camper, and a similarly small amount with wheels other than factory. I don't think it is because Germans are boring, but more that legislation almost outlaws such risk (compromise if you like) taking.
I hang out in the whole forum, in the hope my extensive knowledge within the motor industry, and over 26 years experience of owning and running T4's (not to mention a huge library of related information) may be of help to others. I also enjoying seeing what others are doing, I don't have all the answers, but am lucky I can get the correct ones .................. why do you hang out here???
As I always say, if the knowledge helps then great, if people chose to ignore it; it's not a problem for me either.
Finally in relation to the wheel bolts, it is true there are a couple of variations, mainly for wheels we do not see here. I have never tried fitting Audi wheels (that may come as no surprise to you), but I imagine mostly being 'car based' it is probable that bolts with a smaller 17mm head may be required; to give clearance, especially for an alloy wheel impact socket (even a thin wall one). A quality bolt with the correct radius seat, and thread length of course, should not compromise the wheel security.