In an earlier post,it was stated that Russian de-icers know their work,well don't count on it.Last Nov de-iced in Novosibirsk,after inspection of deicing,noticed large areas on wing (one in front of engine ingress path) & tail missed,told them to redo ,then they sprayed type 4 all over the windscreen (after being told specifically to not de-ice fwd of main door)
Concerning increasing rotate speed,be carefull if obstacle limited,you might not meet your obstacle clearence heights,however no obtacles no problem,with sufficient runway length,
A retired colleague had an interestig experience flying a BAC 1-11 for Ford Air out of Stansted some years ago,inspected wing,found snow on wing but very dry snow he could blow off,so he thought to himself the snow will just blow off during the t/o roll,I don't need to de-ice..... On T/O at rotate speed pulled back,nothing happened,he then firewalled the throttles(you can get away with that on Speys as they have governors) accelerated another 30 kts & staggered into the air.He lived to fly another day,moral of the tale;ANY contamination on top of the wing DE-ICE!