No the white smoke stopped after about maybe 70% of the can had gone in, leading me to believe that it was some kind of crap out of the engine being burned off rather than the spray itsself. When I repeated the operation about 6 months later, there was virtually no smoke at all, so I guess it didn't build up much crap in that 6 months. It clearly did something, but it's a bit hard to tell in a totally unrefined ex-military diesel Land Rover.
No the engine didn't really struggle with the spray going in, I just used part throttle the whole way through and didn't need to increase it. I did rev it a few times but that was mostly to send massive clouds of smoke down the street in an entertaining manner.
Top tip, if you do it get someone to sit in the car with their foot on the throttle. It's murder trying to hold the throttle open and spray a can for about 5 minutes crouched under the bonnet.
