L2 cache is the cpu's own memory. Technically bigger cache is better but not that much. Take E6300 for example overclocking it to 3Ghz and it becomes faster performance than the X6800, even though it has half the L2 cache of that of the X6800. So using certain memories do not compensate the L2 cache , nor increasing it's quantity.
Usually high performance pc of today, requires 2Gb of ram for gaming. It also depends on the system and what you use it for. If you use regular pc for internet and related stuff then a low-end generic ram would be good enough. You would only need 512Mb for regular pc use like browsing and office stuff.
For high-performance and gaming pc, 1Gb would be enough but for better gaming and higher res, 2Gb would be needed. Also if you overclock your cpu, it's good to get them high quality rams from Corsair, OCZ, Mushkin, etc. 2x1Gb rams for overclocking like DDR2 667 and 800 can be purchased for around $250.