e1405 RAM Upgrade

I realize that Dell states the maximum memory for the e1405 is 2GB, but I have seen posts by people successfully installing up to 4GB of RAM when using the most recent BIOS firmware. I have a client that wants more than the 2GB they currently have. If I perform the upgrade, in what way would I be getting the best bang for the buck...

Should I upgrade one of the 1GB modules to 2GB to give a total of 3GB in the laptop? I realize with unmatched modules, I will probably only get about 85% efficiency so would not have the true power of 3GB. Or should I go with 2x2GB for a total of 4GB, which in reality only leaves me with 3.3GB of usable memory.

Any thoughts on this would be appreciated.

Thanks,
Merg