The problem I keep having with your posts is that you're basing your entire experience with s60 as a whole on your problematic 7610 and E50. A lot of users don't have anything like the problems your experiencing, with the phones you use or not. Since you went through your list of problems again, I will go through them too.
1. I'm curious as to how many contacts you have? It also helps a LOT if you leave your contacts open instead of closing it when you're done. My N73 accesses my contacts instantly, and running through them to edit them was just as fast on a quick test I just did. Then again, I only have 130-150 contacts or so.
2. This problem seems to be consistent with only the E50 and your specific firmware. I don't know anything like a phone freezing entirely and reverting to speakerphone as soon as a call is connected. You said it was also difficult to reproduce, so how often does it happen?
3. I've never heard of something like this either, unless you're on a call for over 3 hours.
4. First of all, you can press the power key and scroll to "Remove memory card" if you need to do so, which is much faster than going through folders. Second of all, it's not necessary to get a memory card directly from Nokia either. There are cheap brands out there that cause a reduction in phone speed, errors, and glitches. What brand are you using? I'm currently using a 2gb MiniSD from SanDisk, and I haven't had any problems with it whatsoever. It's fast and reliable as the day I bought it.
5. The N73 (and others) has a 240x320 resolution screen, which also happens to have a larger font size than screens with 352x416 resolution. Fortunate for you and anyone else with bad eyes, Nokia has dropped the 352x416 resolution for all of their upcoming models and has no plan to use it again. It's QVGA and VGA (hopefully soon) from here on out.
I really really like the 6133. I love how fast it is and I really like the overall look of the phone. I would use it in a hearbeat, but I would lose WAY too many features from s60 to ever be able to give it a try. I would have a much lower quality camera, I would be limited to Opera Mini (which is lame), I wouldn't be able to retrieve my emails on it because of the low internal memory, the battery wouldn't last me nearly as long, and I wouldn't be able to open and edit Office documents on it, much less listen to music while I do it. And yes, if I'm away from my computer, I can access and perform all of the tasks I mention without the need for a laptop on my N73. You should venture outside of the E50, specifically the one you own right now. It seems to hate you.