What Nubcake said about the bearings having no extra load, that is why you are using the spacer to get closer to the OEM offset. I do agree with you that the extra long wheel bolts might be a weak point but I don't have data to back that up, I'm too lazy to search. I've been running BBS RS-GT wheels in 19x8.5 et32mm but using 10mm spaces and 45mm longer Cone bolts. With the BBS's wheels, the flange is thicker and just adding 10mm to the stock bolt size (27mm I think) wasn't enough, I had to go longer.
Just got a good deal on Titanium bolts, Cone 45mm from ECS tuning for the RS6, and Ball 27mm from USP motorsports for the RS5. I imagine it will take my 0-60 down by a whole second....right???