No need to try. There is a usenix paper with perf comparisons here => https://www.usenix.org/system/files/conference/usenixsecu...

The paper is about kGuard but they do perf tests against vanilla and PaX.
For latency in syscalls (in microseconds) they wrote :

> The PaX-protected kernel exhibits a latency ranging between 5.6% and 257% (average 84.5%) on the x86, whereas on x86-64, the latency overhead ranges between 19% and 531% (average 172.2%). Additionally, (..) overhead for process creation (in both architectures) lies between 8.1% to 56.3%.

For sockets and pipes bandwith degradation agains vanilla they wrote :

> PaX’s overhead lies between 19.9% – 58.8% on x86 (average 37%),and 21.7% – 78% on x86-64 (average 42.8%).

But the slowdown is much less noticeable on macro benchmarks. For instance the test to build a vanilla kernel :

> On the x86, the PaX-protected kernel incurs a 1.26% run-time overhead, while on the x86-64 the overhead is 2.89%.

And sql-bench slowdown agains vanilla :

> PaX lies between 1.16% (x86) and 2.67% (x86-64).