"I have seen it dynamically compress and serve at a sustained 2.7 times per second a small webpage"
You should be able to get a lot more performance out of a Rasperry Pi 3 than that! It has similar capacity to the 2000-era workhorse Sun E450 https://fanf.livejournal.com/141066.html
So it does seem the bottleneck here is the writer's Internet connection.
If you can use USB 3.0, saturate a GbE link or use lots of memory then the Pi 4 is a big upgrade.
I think this is a good time to plug the webring for geeks, just what you should join if you're running your website on your home connection! http://geekring.net/
I’d caution people against running any kind of controversial thing on their home network. All it takes is a few complaints against your ISP and it will disappear unless you have some business account, and even still.
I'm not going to remove SSL, but I'm surprised it is such a big part of the page load.
https://www.raspberrypi.org/forums/viewtopic.php?p=1705614#p...
The 64-bit versus 32-bit thing is almost certainly software wonkiness, as that forum post indicates. There's no reason the 64-bit mode should be slower than 32-bit mode for that task, and benchmarks often show that 64-bit ARM is actually measurably faster than running in 32-bit mode, due to the additional available registers and whatnot.