You will be very happy with 5.1 then. My current battery stats (on a 4S running 5.1b3) are 1h31 usage, 1d18h standby, 66% battery level remaining.
In my experience at least, beta 3 has the battery life gremlins with the 4S properly nailed. With 5.0.1 up to 5.1b2 I was getting up to about 1.5 days; now with beta 3 it's up to 3-4 days depending on how often I use the phone.
With the earlier 5.1 betas the drainage on idle was more or less sorted. The only thing that continued to drain was when in a low signal area (which happened to be my house - d'oh!) of about 2-3% an hour, but great in good signal areas. Now with beta 3, there aren't any such fringe-coverage battery drainage problems anymore. Battery is now every bit as good, if not better, than my iPhone 4 was.
Note - I'm not the sort that's glued to a phone all day, nor do I game; but I do use Siri a little over the course of a day. As for settings I have the following on all the time; 3G, wifi (with APs at home and work), a modest collection of location services, and two push accounts.
