For FSX you really really want more. Take a look at an Intel i7 Haswell chip (4770k if you can). RAM you can stick with 4gb, since FSX cannot handle more than that anyway. As for your Graphics card, I am not sure about GTA but FSX runs far far better on NVidia. Hyperthreading doesn't matter at all for FSX and I am not sure that it would for GTA. Hard drive space is fine, but if you can afford it and your pc can take it, an SSD will do wonders. If not, try to get a 7200rpm hard drive.
I run these specs on my laptop with the following mods in FSX and GTA:
Laptop:
3.8Ghz Intel i7-4810MQ Quad Core
16Gb Hyper-X Genesis RAM
750gb 7200rpm Western Digital HDD
8Gb NVidia 880M Graphics Card
Windows 7 Ultimate x64
GTA:
LCPDFR 1.0d
ELS 8
DoubleDopplers Met Police Cars + London Mods
ENB (but playing with these)
vDH Police Helper
FSX:
Acceleration Pack - MUST HAVE
PMDG 737
ORBX Global
REX
FSUIPC
AccuFeel
Heathrow Ultimate
The performace in FSX ranges between flyable and fantastic. However, I have spent many hours adjusting my fsx.cfg file to get that going. Very important you do that.
With GTA, being such a poorly optimised game, the moment I put mods on it really starts to suffer. However, if you are careful with what you put on, you can get a decent 40-60fps, with lowest dropping to 20.
Hope that helps you out a little!