Hello, I just built my first system a couple months ago. Here are the specs:
ASUS P7P55 LX LGA 1156 Intel P55 ATX Intel Motherboard
Intel Core i5-760 Lynnfield 2.8GHz 8MB L3 Cache LGA 1156 95W Quad-Core Desktop Processor BX80605I5760
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL7D-4GBRM
ASUS EAH4870/2DI/1GD5 Radeon HD 4870 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFireX Support Video Card
Western Digital Caviar Black WD6401AALS 640GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive
What the system is used for:
1) Video Games. Usually nothing cutting edge. Fine with playing games on medium if needed.
a) example of games: WoW, Civ V, Mass Effect 2, Dragon Age
2) Usually have two people signed in. One side usually has a browser open with a couple sites up while the other side might have a game running.
My question is, for my system what would be my current bottleneck? The reason I ask is that newegg currently has my RAM on sale so thought about doubling it but only if it is going to add much performance to my system.
You likely won't see much improvement in performance. The most stressful thing you're doing is gaming, and the bottleneck for that is almost always the GPU. Sometimes it's the CPU (depends on the game). It's hardly ever the RAM.
Unless you're doing some heavy rendering or encoding, you don't need more than 4 GB of RAM.
As is usually the case if gaming at 1080P or above, 85% of your framerate results (or lack thereof) will be determined by your GPU...(if at 2560x1600, more like 93%!) If you game at 1280x1024, the combination of gpu vs. cpu scaling is a little more complicated, but, progressively more cpu scaling does occur at lower resolutions....
Adding more RAM isn't going to help much, if at all. The main thing that 8GB would help with are if you're doing large-scale photo or video editing, things like that where you're working with multiple large files and large programs at once. Games will run exactly the same at 4GB as they will at 8GB.
As for a "bottleneck" ... you shouldn't really have one on that system unless you're playing at a high monitor size. The HD 4870 is the least modern component in your machine - but it and the 4890 were the best of the 4000 series, and still perfectly capable of playing any game you can buy. I did notice mine bogging down a little when playing some games at 1920x1080, but it was by no means unplayable.
As others have said ... in an otherwise balanced system, the GPU is usually the limiting factor in gaming. But unless you're having noticeable problems with performance right now, to the point where you're unhappy with the results, I wouldn't bother upgrading anything. In terms of the quality of your gaming experience, the difference between getting 30 FPS and 50 FPS is none at all, in my opinion.