@pors thanks for testing this stuff. The core maintainers of go-ipfs are really busy right now but will be coming up for air very soon and the info you're gathering will be useful. We want to do lots of optimizations over the coming months. The issues you're surfacing will help us target those efforts. First on the list is to make IPNS a lot faster -- a couple people are already working on that one.
If you figure out ways to reliably reproduce the slow response times, I'd say go ahead and submit a bug report on https://github.com/ipfs/go-ipfs with instructions on how to recreate the issues. That will make it easier for the committers to keep track of it, and to let you know when it's been addressed.