Need advice on laptop as a replacement for desktop and getting it from US to India

remove the box, install a few programs, create/save a few documents, so that if customs does open it up and inspects it, it doesn't feel new.
Mail the receipt so it's not physically on you, The receipt is a dead giveaway it's new.
But, take a picture of the receipt and keep it in your phone. that way, if they do conclude it's new and decide to charge you import tax, you can prove the value. (otherwise, they'll inflate the cost significantly, so the tax will be higher)

They can't charge anything if he says it's his posession.

Also "M" or no "M", a dekstop GPU will always be stronger than a laptop one. They didn't put the "M" to this years mobile GPU's but they still have lower clock rates.
My personal opinion is that I strongly suggest you to build a desktop. You can just order a monitor from Amazon, I bought a lot of monitors from Amazon US and had no trouble at all.