I know this isn't anything to write home about, especially on this site, but I just finished sequence 5 in my second playthrough (doing all missions at 100% sync) and I managed to assassinate the Banker without anyone noticing I was at the party. I've seen videos of this done before but I had never figured out a good way to do it. Anyway, I just felt really good about it and wanted to post this where someone might appreciate it.
I killed the guard near the hay bale where you start then used the courtesans to occupy the other guards. I then walked to the far side of the party, sat on a bench until the Banker and his bodyguard turned away and then shot the guard with a poison dart. Moving up one bench, closer to my target, I waited until the poison took effect and the Banker came my way. While the party was distracted by flailing arms and big boobs the fat man was blissfully oblivious.
It felt pretty awesome killing him from the bench, watching the death monologue and then coming back to reality to see the Banker "sleeping" with the rest of the party going on none the wiser. I then calmly walked/blended my way over to the nearest leap of faith and proceeded to casually stroll out of the area. It was awesome. Prior to killing him I had taken out all the guards on the roof too. It didn't really matter but it added to the cinematic quality of the assassination. Literally no one saw what I did.
Nice work. Now try it again, this time without killing anyone. Trust me the satisfaction is 10x higher.. for about 20 seconds I guess