Using AES with GMAC I can clock from 2-4GiB/sec/core on typical laptops and over 1GiB/sec on phones. The Apple M1 does almost 5GiB/sec/core. Gen10 and newer Intel CPUs with VAES have produced benchmarks in excess of 10GiB/sec/core, which means a single core could theoretically saturate 100gig fiber if it were just doing crypto.
Of course nothing stops CPU makers from adding ARX accelerator instructions, but I have yet to see any proposed. If constructions like ChaCha and BLAKE2/BLAKE3 get popular enough I could see this happening.
We don't have to derive the answer to this question from first principles. It's an empirical question.
Note that thanks to AES-NI vectorization (an example of hw acceleration I was referring to) it reaches more than 16Gps/core on the same test on Icelake.
Those numbers can grow up to 50% for big packets (1500-bytes and higher).
With a high performance stack, IPsec (and Wireguard for that matter) workloads are limited by crypto performance, not packet processing performance, and the perf difference between IPsec with AES-256-GCM and Wireguard is basically the perf difference of AES-256-GCM vs Chacha20-Poly1305 of your platform.
And the main reason is the cipher: one is hw-assisted (AES-NI on x86), the other is not.
Again, I do think Wireguard is nice because it is a clean sheet design with good choices and it "just works". However when I hear "Wireguard is faster than IPsec" it is not true in my experience, and can be easily explain by the cipher choice.
The speed gains wouldn't be as significant. AES uses S-Box computations that do well when hardware accelerated, whereas ChaCha/Salsa20 are designed to use more typical CPU instructions for bitwise operations.
However, AES is hw-accelerated in most systems those days and as a result, using IPsec with AES-256-GCM is usually much faster than Wireguard [1]. Note that if Wireguard was using AES instead of Chach20-Poly1305 I am sure it would be on par, plus I am confident we'll see hw acceleration for Chacha20-Poly1305 in the future too.
So I'd say right now if you need absolute max performance, a good IPsec implementation is much faster than Wireguard.
[1] for example, just running 'openssl speed -evp chacha20-poly1305' vs 'openssl speed -evp aes-256-gcm' on my laptop gives a ~2x speed advantage to AES.