I upgraded from 1gb to 2gb a few months ago when playing bf2, didn't notice a huge difference. It definately lets me alt tab and mutlitask faster. Programs are more responsive when I'm playing a game and doing something else like checking a scoreboard for the server im in. 2gb is going to provide more smooth play at really high res's and detail levels.
In my opinion, 1gb is plenty for lower resolution gaming around 10x7. If you bump a game up to 20x15 You will most likely notice occassional or frequent jerks. Just for kicks I played oblivion at max settings at 12x9, about two weeks ago with only 1gb of my 2gb of ram (I was bored and wanted to play inside my computer) I was surprised that I didn't notice much of a difference, everything seemed to be just as smooth. I was a little dissapointed cuz I wanted to think I was uber cool having 2gb ram even though it's been popular and standard as of late :X ( I also underclocked my processor to 800mhz and tried playing games )
If you aren't having any random jerks where the screen freezes for a split second, then you aren't going to notice a huge ( or any ) difference in 1 vs 2gb in-game. Getting 2gb of 4x512mb would decrease your performance depending on the game you are playing, 2t timings are bad. I would only assume getting in a 64 player server and having ur settings at max at 16x12 on a modern game would be laggier with 1gb.
That article is very misleading. The avg fps might be similar, but the minimal is going to be much worse. With 256mb, you will spend alot more time in the low fps and you will have alot more jerkiness even when you are getting 50fps. in a 512mb vs 1gb scenario, having more ram will result in smoother gameplay for certain games at certain detail levels. Obviously quake 1 isn't going to jerk or lag with 512mb ram.