> It's called marketing, it's not meant to make sense ;-)

;-) To make the improvements seem even better they could as well have the e6500 compared to its ancestor from a decade ago, the e500v1.
But to be not too unfair towards Freescale I will note that while comparing the e6500's performance to e500mc's instead of e5500's makes the e6500 shine even brighter it's the exact other way round regarding the power efficiency comparison as the e5500 is actually even less power efficient than the e500mc. See:

https://morph.zone/modules/newbb_plus/viewtopic.php?forum=3&topic_id=7001&start=435
https://morph.zone/modules/newbb_plus/viewtopic.php?forum=3&topic_id=7001&start=439

So substituting the e500mc by the e5500 in Freescale's statement would read something like this:
The e6500 core enables about 60% performance improvement as well as 2.6 times the power efficiency over Freescale's previous generation e5500 core.

> Sounds like they've taken the e5500 and added in a second thread and AltiVec.

Yes, that's exactly what I think they did to come up with the e6500.

> Sounds pretty much like where the G5 would have gone next.

Yes, considering a "PPC980" would surely have featured AltiVec like the PPC970 and probably been derived from POWER5 which was the first POWER CPU to have SMT capability.