PurplePaul,
600mg a week would be more than enough for me. And it will without doubt help you. But your a fair bit heavier (I'm 95k) also would depend on what your cycle history is like, and the amount of muscle you have built (especially above any beyond what you would hold naturally).
IMO as you reach a certain level you will need more and more AAS to stop the potential muscle loss from T3. I guess form your avatar that you are a PL, so are you prepared to lose muscle or strength to get your weight down.
Please note my opinion only - and no science to back up... Personally I like to use the same amount of AAS for cutting as I do for bulking - and only the choice of meds, diet, training and extras change. For me -currently that is 500mg test a week as a base - and other bits also of course

. so if you usually use 600mg a week, go for it. If you are usually on 750mg or 1g a week I would bump it up - but would depend on your goals and priorities - if the main priority is fat loss and you're not to bothered about strength and muscle then 600mg is fine - could go lower even (500mg).
And just to say before I am attacked...
600mg is a load of test. And runnig this alongside a T3 Cycle is more then enough to negate the potential catabloic effects. I am really questioning your goals as if you are a competeting lifter your gear use should not necessarily match that of a bodybuilder. What ever way you are going and decide to go...Good Luck with it.
Peace,
ERGO