I went the same direction, from WordPress to static site generation. I did the same evaluation as you are trying to do and ended up with Hugo, mostly because there is a lot of support available for it. My runner up was Pelican, because I was fluent in Jinja2, but I didn’t want to mess around with the templates and Hugo’s were prettier. Sue me, I am shallow.
The one regret I have about Hugo is that the templating language is challenging. I am trying to be as neutral as possible, but it seemed like even simple things were complicated to achieve. If someone would come up with a Hugo that speaks Jinja2, I’d be really delighted.
Other than that, conversion from WordPress to Hugo was relatively straightforward, despite needing to find a gallery component and converting menus. Hugo is indeed very fast in processing, which become important when your blog has thousands of articles.
I set up the blog as a private git repository. The server pulls from it, then runs Hugo and a full text search engine, and the content is visible and searchable within five minutes on update.
There must have been a gallery component, since I only looked at generators that had one available.
Honestly, in hindsight the templates were really not a big deal. Just for fun, I tried converting the Hugo template I used to Pelican, and it was easy for me.
Pelican is solid and mature and I would use it, in hindsight. The only major flaws are that it’s much slower (but makes up for it with incremental builds) and that the community is much, much smaller. On the plus side, Jinja2 is much, much, much better than Go templating (Hugo borrows from Go).