Hudson a couple of points, I havnt read all the posts fully, so dont shoot me if Im repeating someone.
Your TOW is 45T and your limiting TOW (RTOW) is 70T, you go rated thrust and use the speeds for 70T.
There are if I have grasped you QN correctly a few flaws with this line of thinking. No1, the V1 at 45T compared to 70T, and No2 the V2.
Im looking at this as simply as possible. Your no1 engine ****s itself at 115kts, your V1 for 45T is 110kts, However your using a 120kts for an artificial weight of 70T. So Mr Hudson can you please explain why you decided to abort your takeoff 5kts past V1?
V2, if you have bugged a V2 for 70t instead of 45T, has anyone considered your 2nd segment climb graident, what will you achieve if your flying a 45T aircraft at a 70T V2 +20?, I sure dont know.
I suppose your perf dept may have a reason for wanting to use the higher V speeds at an artifically higher weight. But generally speaking you should be using the Vspeeds for the actual aircraft weight. And anyway if there is such a policy it really should have been explained better during your perf day when you joined. Problem with pilots (and I am one) is that years of BS and C wispers associated with perf have severly muddied the waters.
Your Vspeeds do change when using an assumed temperature, as they will ever so slightly when considering slope, wind ect, but I dont think your question relates to that, does it?
Ok thats me!
Rgds