Grindlay
There is no simple precise answer to your question of how fast would it be going at the top of the ramp because that depends on where it started on the deck and which ramp angle it was using as well as its weight and the ambient conditions which natutally determine the thrust of the engine.
Typically you will not be far out on the weight/thrust issues likely to apply on such a normal service takeoff if you assume a T/W ratio in the range 0.85 to 0.93.
You can do your own flat deck sums by use of the equations of motion which I am sure you know. If not then the ones you need are v=ft and s=1/2f(t squared). V being speed, f being acceleration (which is T/W x g) and t being time. Use whichever system of units you like but keep them all the same.
As for the reduction in endspeed due to going up the ramp (when compared to the flat deck case) it is likely to be less than 3-4 kts and lost in the noise of windspeed over the deck.