While people are waiting on all the GPU stuff to happen, I have a few "real world" performance numbers on the CPU that may be worth discussing. Lostinblue posted some DMIPS numbers above, and it reminded me that I'd done a few calculations in that regard already. Dhrystone MIPS (DMIPS) is a CPU performance benchmark that's been around for a long time, and is commonly used enough that it's at least fairly easy to get Dhrystone values for a variety of different CPUs, so it'll do as a point of comparison for Espresso.
According to
this website, the PPC750 derivative in the Gamecube managed 1125 DMIPS, and ran at 485MHz, so that gives a DMIPS/MHz value of 2.32, which we can use as a loose measure of efficiency of the cores used in the GC, Wii and Wii U. There don't seem to be numbers on Jaguar DMIPS performance (as it isn't out yet), but I found
this page with a benchmark of 5325 DMIPS for a dual-core Bobcat chip running at 1GHz. This comes to 2.68 DMIPS/MHz, so a bit more efficient per clock than the 750, but not massively so. Of course, the Jaguar chip should be more efficient (AMD claims 15% improvement per clock), so it might top out at around 3 DMIPS/MHz. We don't know what changes Nintendo and IBM have made to Espresso's cores over the Gekko/Broadway design, though, so it might be somewhat more efficient as well, but I wouldn't expect anything massive (big changes to the architecture would make BC tricky). Let's stick to a conservative 2.32 DMIPS/Mhz for Espresso's cores for now, though.
So, we're looking at about 8,700 DMIPS for three 1.25GHz Broadway cores, versus about 38,400 DMIPS for the eight 1.6GHz Jaguar cores expected in PS4/XBox3. If MS are dedicating two of the Jaguar cores to the OS, then there's about 28,800 DMIPS of performance from the remaining 6.
How does this compare to the last generation? If lostinblue's numbers are correct, then the Cell PPE managed 1879.63 DMIPS at 3.2GHz, or 0.59 DMIPS/MHz. The XBox360's Xenon was effectively just 3 of these, so that comes to 5,639 DMIPS total (35%
worse than the 1.25GHz Espresso). If anyone has numbers on Cell's SPEs, I'd be happy to add them in here.
Now, of course Dhrystone is only one benchmark, and only really tests certain things, so you're going to get different results with different kinds of code. I'm also using estimates here, so further customisation of Espresso's cores may boost its Dhrystone performance, for example (but don't expect much, I'd be very surprised if it were over 10,000 DMIPS). Nonetheless, hopefully this illustrates how clock speeds are far from the main factor when comparing CPUs' performance.