Do NOT buy anything other than an Intel i7 based laptop. Other than this, it should have 8GB of RAM, a dedicated 2GB Nivdia or Radeon Graphics Card and preferably a Solid State Disk or 1TB Hard Disk. This specification is pretty easy to find from all the major manufacturers and in Australia, such a machine (with a normal hard disk, not an SSD) retails around AU$1,000.
For this price you will get an i7-6500U processor which runs at 2.5GHz and bursts to 3.1GHz.
The next step up is a BIG jump in price to get something like a Dell Alienware with i7-6500HQ (up to 3.5GHz) – 16GB RAM, SSD will cost US$1,700. If you do not mind spending more then spend US$2,600 to get a 4.1GHz model that really is the ultimate in speed.
I run a Toshiba notebook with i7-6500U, 16GB RAM, Radeon 2GB Graphics with an upgrade to 512GB SSD and my original 1TB hard disk is now my secondary storage drive instead of my DVD. The 17″ screen is handy when I am onsite but I mainly work off a 24″ monitor. This is great for normal drawing work but I could really do with a bit more speed for Panoramic 360 renders.
