[Ask] Extra RAM or Hybrid Drive ?

Im about to buy ASUS G53SW - SX080V - with the following specs :

Platform: Intel Core i-7 2630QM (2.0GHz Boost up to 2,93GHz)
VGA: NVIDIA GeForce GTX 460M DDR5 (with 1.5GB memory)
Memory: 4 GB DDR3
HDD: 640 GB SATA
DVD Super Multi
Display: 15,6" with LED backlight (1600*900) 16:9
Web Cam: 2MP
Bluetooth 3.0 | WiFi 802.11b/g/n | HDMI | firewire | gigabit LAN
VGA Out | 3 x USB 2.0 | 1x USB 3.0 | Card Reader
Sound : SRS Suround sound with Altec(R) Lansing Speaker | Weight 3,3kg
OS: Windows 7 Premium

My plan is to have it as a primary gaming machine for about 3-4 months until i am capable of amassing money to build a gaming system. Will use it to work too

My question is : should i upgrade the memory to add an extra 2-4 GB or buy a momentus hybrid drive instead ?

Thanks for your help!