Most servers that I am interested on joining are hosted in Europe/US. The ping on those servers are usually 200-400 ms compared to big mastodon instances like fosstodon.org and universeodon.com (20-50 ms). Would this affect the responsiveness in a noticeable way?
That’s certainly high enough to affect the feeling of responsiveness. It won’t feel as “snappy” as it would without the latency. However, it’s easy for a difference in server-side processing speed to dominate that degree of latency. Lemmy isn’t super optimized and different instances can run on wildly different hardware with different levels of care put on DB tuning.