Its all OK until you have an engine failure in LVP's and you can't look out the window and see and avoid. These machines are in general getting on for 20 odd years old and they weren't very spritely climbing on one engine when new.
Yup. These planes don't achieve the published cruise performance either.
An extra 50kg isn't so bad
As long as you don't take 50 kg of cargo/pax with you.
As for the S.G this can a problem even if you get given one by the bowser man. The S.G tends to get taken early morning. And you have a special bowser that can do over wing fueling. So it can sit out in the sun all day until you refuel. Which is why a lot of us use an SG of 0.77 when ordering. A 500-1000trs is the normal uplift at a time so its won't give you that much extra over. Most of the modern TP's have pressure refuelling and the units I have used anyway pull 50-75kg of it initially which calibrates the S.G. before pulling up to the weight in the panel. And a cross check against the bowser S.G. is usually within 0.01 which would be normal for a bulk to bowser temp rise.
This doesn't happen where I'm from. When I call in for fuel I ask for the "batch corrected density". That is the density of the batch in the fuel truck which is corrected to 15 degrees C. The truck also meters at 15 degrees C. Today the batch corrected density was 0.819 kg/litre - which means that if you have a litre of jet fuel and the temperature of it is 15 degrees C, its mass will be 0.819 kg. That will not change as long as nothing is added or subtracted from the fuel truck - temperature does not affect this number! So if I want 500 kg of fuel I take 500 and multiply by 0.819 to get 409.5 litres. If the fuel temp is 15 degrees C then the actual volume pumped into the tanks will be 409.5 litres. If the fuel temp is greater than 15 then the volume pumped in will be greater, and if the fuel temp is less than 15 then the volume pumped in will be lesser. Whatever the case, I know that I will get 500 kg of fuel. I can use 0.819 throughout the entire day as long as the fuel is coming from the same truck.