Originally Posted by GameBoy
Yeah, there are differences between all three. The HX650 is an older Seasonic S12-E design, the TX650M is a newer CWT (PSH-III I think? Let someone else confirm this) design, and the GS600 is a PSH-II. The performance on all three of these units are fairly close, though, and all probably fall under the "decent" category.
Why are you asking?
HX -> CWT DSG(High end platform)
TXM -> CWT PSHIII(new mainstream platform)
GS -> CWT PSHII(solid platform)
Performance wise HX > TXM > GS
Quality wise HX > TXM > GS
Value wise(newegg) TXM > GS > HX
Or you could just go with an antec TPN which is on par with the HX on everything except efficiency but price wise it fights the TXM so it holds a lot more value than all of the above.
Haven't checked if it's still available but the Cougar GX700 was today's sheel shocker at newegg @ 60$ after rebate which made/makes it a helluva deal, so if it's still available grab that, if not grab an Antec TPN.