I've 24GB of RAM in my MP 1,1 which I sourced from eBay - they are Micron modules with thin heatsinks. I've had no issues with them, nor noticed fan speeds ramping up any more than usual.
Regarding CPU upgrades, the x5355 CPUs (2.66Ghz quad core) you can get for < $50 pair, the x5365 (3.0Ghz quad core) still are < $150 for the pair. One day when they get closed to $100 I'm going to bite, but they would only give a meagre performance increase over 2.66 parts anyhow.
JB
Regarding CPU upgrades, the x5355 CPUs (2.66Ghz quad core) you can get for < $50 pair, the x5365 (3.0Ghz quad core) still are < $150 for the pair. One day when they get closed to $100 I'm going to bite, but they would only give a meagre performance increase over 2.66 parts anyhow.
JB