Thanks Keith, I hadn't checked it in CAP 698, I guess that makes it a question more specific to the TriStar.
Thank you also JT. CAP 698 is a UK CAA publication used for the ATP exams, its a B737. The TriStar had/has separate methods to calculate increased V2 TOM for both WAT and obstacle limits but it might have been what you suggest. The only thing possibly against that arguement is that the aircraft brakes were not brilliant, you could get VMBE limits on take-off at high weights and temperatures.