High Sierra is performing very well for me, I am very happy with the whole experience so far. Please see my signature for hardware details.
During beta testing I was paying close attention to Activity Monitor and there are a huge amount of processes running as compared to Mavericks (which is what I was running previously), but the system seems to be handling the memory very well. During normal usage with Mavericks I would frequently see my “memory used” climb to 10 or 11 GB, but now it seems to hover between 5 - 6 GB “memory used” and I have not seen it go above 7 GB (maybe it did and I did not notice). After installation of the official release, everything is very much the same.