The new Samsung-made Nexus 10 uses the next-generation Exynos chipset - an Exynos 5 with two Cortex-A15 cores at 1.7GHz and Mali-604 GPU (the same chipset as the new Chromebook).
So, rumors that the next Samsung Galaxy S IV will use an Exynos 5 chipset should come as no surprise, but the rumor is dreaming bigger than we would have thought. It points to the Exynos 5450 - with a quad-core A15 processor, clocked at 2GHz and a beefier Mali-658 GPU.
We already saw early benchmarks of the 604 (which is a quad-core GPU), so the 658 should be wipe the floor with current GPUs (it's an octa-core GPU). We have yet to see Cortex-A15 benchmarks but it should easily top Krait's per-core performance.
Now, there's a bit of a problem - power usage. With four Cortex-A15 cores and eight GPU cores, even a big battery would be drained pretty quickly. The Exynos 5450 will be made on a 28nm process (instead of 32nm as the Exynos 5250) and the CPU will probably be downclocked to at least 1.7GHz, but even then battery might be an issue.
Anyway, we wouldn't be surprised to see an Exynos 5250 inside next year's Galaxy S flagship, but the 5450 - as awesome as it would be - might be be too much to ask so don't get your hopes too high.