Jenaway: From my experience: OpenCpn
will run excellent on "ANY" laptop
sold after 2004 with minimum 1 gig ram, even without a harddrive, just running from a USB menorystick with Xinutop linux Marinux Website
. Also, It will run fine from a low spec waterproof Samsung GT-S7710 android mobile phone
From there, you can go for more fancy and expensive solutions with specs "X" and "Y", but in real life it will not bring you any navigational advantages over the low cost samples mentioned above.
Important things to consider if shopping
is power consumption
, mounting position, daylight visible displays etc etc. If you choose a PC based platform and want to have a NAV computer and not a "for everything PC" save the 2k and go for the low cost solution with Xinutop.