iPhone 4 seems like it took a hit with iOS5, but it's still fine for me. People who have impressions for it during the betas are just posting heir own experience and it can be entirely subjective. It's not like they were benchmarking it or anything, so your experience may vary. If you feel let down its not their fault.Have you used it on a 4 regularly (daily) or just a 4S? It's not apparent until I actually have to start using the phone, wheras some things begin to chug.
I sure hope it remains as you say, because as someone who owned a 3G and updated to 4.0 I've always been wary of their optimization on older devices (which should be dead simple for apple, they can count the number of specific devices to update on one hand!)
That said, iPhone 4 runs fine on iOS6 for me.