It would help if we knew what motherboard and CPU you'll be using. The Patriot requires a lot of voltage and it isn't appropriate for a Core i5 system.
on a side note, the first pair of RAM you posted (Patriot) look like very good modules but do not know if they are supported by that board (Bios). Even though they have the same specs as the G.Skills you have to make sure they are compatible before you purchase.....
To follow up I recall from reading threads that you want to buy the right clock speed. Or else its a waste of money ? I know I have simplified that statement but I do want to oc this board and processor at some point I just didn't know if i would also have to oc the memory. I was looking to buy 3gb but if i need 4 i'll get 4
If you have Xp there is no need to get more than 4GB, if you have Visa or 7 then you will be fine with anything around 4GB or above.
The memory does not need to be overclocked, if you want more speed from your ram then raise your FSB a bit but don't expect anything major...I have been able to overclock to 4Ghz w/o touching the ram, just FYI ....