Its not. Its about to compare with SW max blocksize. So you can say 1.7 or 3.6 I dont care.
No, it will not. As far as computational resources go, SW 4 MB requires less than a 4 MB block size increase would. The increase with Segwit would also be gradual with adoption, which is what makes it better.
I see. If this is the only viable point you can find in summing up miners costs and benefits we can aggree on any size here. Miners benefits for buying SW will not increase dramatically in this comparision.