Through freecycle I've acquired a couple of SIS motherboards. One is a 661GX mobo with a 2.93ghz celeron, and the other one is a SIS 760GX mobo with a 3100+ Sempron. Both will run Win98, but which is better?
The 661GX supports the P4 Extreme Edition CPU, and 760GX supports Athlon 64 x2, so I suppose the 760GX is the better one?
I'm just after a bit of guidance as after P3 and Athlon XP I loose track.
Given that a So754 system has memory controller integrated into the CPU and an (early) So775 system has memory controller in the chipset, this is comparing apples and oranges - the differences between the platoforms are far greater than the differences between the chipsets. An So754 Sempron will generally be superior in most regards to a So775 Celeron, regardless of the chipset involved, but for Win98 both are complete and utter overkill.
Something to note is that there are no Athlon 64 X2 processors for Socket 754, although OP might have a s939 or sAM2 760GX board that I don't know of.
There were some 760GX boards with So939 too - not too surprising given that an Athlon64 chipset just connected to the CPU's Hypertransport bus, regardless of what the CPU did with memory. Theoretically you could even have an AM2 or 3 board with 760GX -in fact good chance Asrock made one 😁
(I have an Asrock nForce3 board - essentially the same generation as the 760GX - with an AM2+ socket hosting a quadcore Phenom II AM3 CPU)
