Well, even with GMP, it’s guaranteed to be slow. Good enough if you need a dozen numbers or so.
Secure engine is mostly unaffected by the choice of backend (except for nextInt() case)
With GMP installed, all engines are approximately 400 times slower than native
Mersenne Twister is consistently 400 times slower than native, whether you use GMP or not
PCG is 100 times slower without GMP and xoshiro256** is 50 times slower without GMP
100-150 times slower than native
GMP presence does not affect performance that much, but PCG will run twice as fast
JIT helps almost as much as GMP (use both for max performance)