I have no idea about mobile cards though. Personally I run a duel core laptop with an old as hell AMD Radeon, and I then OC it through the freak'n roof! It played SRTT on medium to high settings....which is amazing since it barely played it on lowest settings un OC'd.
So far, my Alienware M14x with a "GeForce GT 555M 3GB DDR3" graphics card can play SRIV on "Ultra" setting. Though, I want to try it on GTAV. Which I'll have to wait for PC release, hoping it to be released ASAP. I've noticed that there are new Alienware laptops release, Alienware 14 with a "GeForce GTX 765M 2GB GDDR5" and Alienware 18 with a "GeForce GTX 780M 4GB GDDR5 - NVIDIA SLI Enabled".
Also, I have no idea what are those "DDR" or "GDDR" means. Anyone?