The confusion is understandable as well. These manufactures really need to stop listing Mhz on any part as a blank statement. "3.4Ghz CPU" can go back to a 550, and not work with anything past that...including the 650 of the same Pentium4 family of that recent era.
The chipset family support should be listed, and specifically. As in " up to Pentium4 5xx series" vise just listing MHz.
And that's just the CPU. More often than not, you still see folks confused on memory MHz no matter what platform they're working with. The memory MHz pie can be split up 10 different ways, and still have some assumption left to ponder.
But ya, the 915 chip only supports 5xx CPU's which are single core, and if the max is 3.4, it stops at a 550 (maybe a 550J?). The 925x/925xe only support the 5xx family as well, but introduce the 8xx dual cores too. No 6xx/9xx though...that's for the later chips.