I can't speak about these benchmarks (the site is down). But Meltdown is not about speculative execution, it's about out-of-order execution. The fixes for Meltdown involve getting kernel data out of user virtual memory, and flushing the TLB if the processor does not have the pcid instruction. So context switches - including system calls - will tend to be more expensive, and if the processor does not implement pcid, way more expensive.

See https://meltdownattack.com/. I haven't yet read the Spectre paper, but I can say that the Meltdown paper is very readable and walks readers through everything. I anticipate the Spectre paper is as well.