Hello, to start with a note on RAM... not all PC RAM is Msc compatible, even if the same rating.
667 may work at 533, depends on the prgramming on the chip.
G5's need RAM in Opposing Pairs. The Quad can use ECC or non-ECC, but I think it all must match. Heres some...
Faster RAM in a G5 does nothing for performance, know that.
The controller only operates at 533 MHz.
If the RAM is of the correct density and spec, it should work. The most common side effect of using PC2 5300 RAM is the System report lists the RAM as PC2-3200.
This is due to incompatibility in the EEPROM, but shouldn't effect performance.
Get a PPC Mac compatibility guarantee.
PPC Macs require APM within the drive format for bootability.
APM has a drive size limit of 2.2 TB.
If a drive is formatted in GUID, there is no size limit, BUT, the drive isn't bootable.
Also know that the G5 controller does not accept all SATA drives equally, especially the SATA 6.0 Gbps (SATA rev. 3) drives.
Some will require a jumper to limit data rate, some will auto negotiate, others won't be seen.
GoodOldMac.... For Your money, the best upgrade with noticeable right out of the box improvement you can make to your PPC mac is to install a SSD drive. Solid state! While more ram helps when working with a massive file it really does nothing for your read write speeds that is going to be limited by your hard drives capability.
I just installed a Samsung 840 120gb SSD from microcenter usd$79. on sale.
I used the ssd to house my os and applications. All of my apps now open within 1 to 3 bounces boot time is almost20-30 seconds faster from power on to login.
Im telling you the best bang for your buck is the SSD upgrade. dont get yourself confused by some retail store geek who gets a woody about how maxed out his machine is on ram.