The bottom line is that FSX - and other flight simulators - simply need raw CPU horsepower (high clock rate), fast RAM, fast storage (more storage than you imagine!!!) and a powerful graphics adapter. All of this has to be tied together by a fast data bus.
It is impossible to cram all of this, plus the required cooling, into a laptop.
With a laptop, you will be able to run basic FSX, and that's about it.
You will, after a couple of months, be frustrated out of your skull, because all the nice add-ons that you would like to have, even the freeware ones, demand more horsepower than your laptop can supply.
And you will then be frustrated that you spent all this money on your laptop, where you could have used it in part for a decent desktop.
Jorgen