You seem to be assuming that IBM will use the PowerPC 450 chips that BG/P uses. Sequoia will instead use some not-quite-yet-disclosed 45 nm part with a much higher clock rate.

Cray ran HPL only on the XT5 for Top500. Unlike the earlier press release about the 1.64 petaflop machine, which is a combination of XT4 and XT5 cabinets, the peak listed at Top500 is 1.38 petaflops. This is accounted for solely by the 200 cabinets of XT5.

PDE is intermediate level calculus.

The PDE that you took as an undergrad is indeed intermediate level calculus. That's not the PDE the OP is talking about. Graduate level is an entirely different creature. Full of scary things like Sobolev spaces, weak derivatives, semigroups, and the myriad types of existence and uniqueness proofs, I'd bet you would not recognize the majority of the questions on the OP's exams.