Whats the width? on ET50 if its an 8" wheel then compared with a standard Monza it will stick out 7mm more. If its an 8.5" wheel then it will be 14mm more.
My wheels are 15mm further out than standard Monzas because I've got an 8" ET50 wheel with 8mm spacers and they are perfect - I just had to do the little wheel liner modification and I've got absolutely no rubbing on my Eibach lowered car.
So you'll be fine with ET50.
If you go with ET45 you'll be in trouble on an 8.5'' wheel (it's 19mm further out than a Monza) and on 8" you'll be an extra 12mm which will be fine.
Personally I'd go for the ET45 wheel in 8" (if you can) then you could add a big brake kit later without having any fitting issues.