Although a really rough number you could compare MIPS(million instructions per second:
Xbox360 IBM "Xenon" (Triple core) 19,200 MIPS at 3.2 GHz
PS3 Cell BE (PPE only) 10,240 MIPS at 3.2 GHz
AMD E-350 (Dual core) 10,000 MIPS at 1.6 GHz
AMD Phenom II X4 940 BE 42,820 MIPS at 3.0 GHz
Intel Core i7 2600K 128,300 MIPS at 3.4 GHz
Now since Jaguar is rumored to be 20% faster than Brazos(e-350) and an 8-core cpu you would get:
PS4/Xone Jaguar cpu: 48,000 MIPS at 1.6 GHz
That would make it in theory faster than a AMD X4 940 wich is really not that bad, considering that they can offload tasks to the gpu easily.
In games today cpu speed jsut isn't that important, especially not if they can optimize like in consoles(a one chip design has way more benefits):
