Wow,
I didn't think this subject would stir up anything like 3 pages worth of discussion. I have spoken at length to various peeps in my company and also studied my sim prep and it would appear that in this case the question is moot as the profile itself prohibits assumed temp takeoff as the runway is contaminated but the discussion has been very useful to see various sides of the argument.
The simplest mental picture I have should the same profile be put but at an assumed temp is that I do what the book says and simply adhere to the 5 min limit then set MCT. In many cases this gets me more thrust but in the odd occasion with low assumed temps then it might well mean a reduction. As at this point we are down to one engine I would suggest that not kicking the wotsits out of the other one unnecessarily would be preferred to creating a 100Tonne glider.
I started this thread to see if anyone knew of any actual paper document that says where assumed temp is used then the limit is out but this fabled document seems not to exist so I will personally be going for MCT at 5 mins and passing my sim check (hopefully)
May thanks for all the contributions