You will exceed the rating still. If you bikes come off at 70mph will your insurance company cover the the pile up on the freeway? I dont think so, you did not follow the manufacturer recommendations. Would you want your significant other following behind you when this happens? Do you want to pay for the new ebike even if you dont kill anyone?
ok enough of the scarry stuff. Your rack has limitations at many different points.. total weight, the weight on each contact point to the bike, cradles, arms , clamps, straps . Each one is only designed for a 40 lb bike. If anyone of those fail the whole system fails. The bike starts to fall. i have had a bike flat tire once when i was underway in my rack, fell half way off went across 3 lanes of traffic in a split second very scary, made it off the hwy
A second time one of my clamp arm had gotten bent and I did not realize it , came off 3 times in a short distance while driving from Ga TO DC .
I personally do not think that saving the money on the rack is worth peace of mind and the additional safety.
I ended buying a van just because of the ebikes, I didnt like the rack for long trips even done correctly..I enjoy my $35G "bike rack"
Weigh you bike , do not take manufaturer info to be sure