do 500mg... Course it depends on how much T3 you use... But 250mg of test a week is hardly anything, it doesn't have much anabolic power to counter the T3.
You are better off using a much stronger steroid and using the T3 at a higher dose for a 4-8 week period. Something like testprop/tren. Or the oral route, something like Halodrol or Epi or even "tren" for around 6 weeks at good doses.
A low dose of Test + T3 will work but if you're going to go on cycle and suppress yourself it's about the least effective cycle you could run.