It's not just the ET that will affect it, the style of wheel will as well. The offest is measured between the centre of the wheel and the mounting face but the shape of the spokes is also a factor and that can only really be tested by fitting the wheel. The other thing you don't mention is the wheel width... In theory the same size wheel and offset would fit if it's the same width (but like I say, not guaranteed) If you went for a wheel with a higher offset you could get it to fit by using different sized spacers (or you could go for an offset a few mm lower with no spacer)