As a general rule of thumb, split memory sticks always work better than a net total, i.e. two 512 mb sticks will perform better than a single one.
Why?
Think of it lust like an electrical circuit. A long chain of bulbs in a series circuit will glow dimmer than if they were in a parallel circuit.
Similarily the computer system accesses the RAM in an automatic manner, if there are two or more sticks, they will be accessed parallel.
Now say in a series circuit 2 bulbs of 10watts are running simoultanousely(dont know how to spell that). , Now in another circuit, which is parallel, there are two 10w bulb glowing. If you compare the bulbs, the ones in the second circuit are giving out more light while the ones in the first are giving out less light individually.
So in computer terms, if your RAM sticks are in parallel they will perform better.
In my uncle offfice, he controls a set or 120 servers. Now since computation is very important and there is zero tolerance of errors or low performance, servers ship with upto 10 ram slots, now instead of having 10 GB ram, many of the servers only have 128mb per slot giving a total of only around 1GB. Performance, its only about performance.
Now since youve stated, that you are a fairly light user with occasional games and are too a light consumer of computer devices, single sticks with maximum memory is the best option, it will save lots of money. Besides all my evidence, buying separate sticks only will give you a performance boost of up to 30-35%!....not much but critical to hard core processing systems.
So best if you buy big chunks of RAM in one go. Happy buying