Currently trying this patch out also, definitely feels like an improvement; we'll see when the day is over. I usually get about 6-7 hours (w/non-patched RB) though most my files are about q5/q6 ogg, and hardly ever use the headphone-out (always the line out with my headphone-amp or if I got it plugged into the aux-port of my car radio).
One thing worth to mention if we compare different file types:
On a x5l with vanilla rockbox I get 15.5 hours playtime for MP3@128k and 14.5 hours for OGG@Q6. A difference of 1 hour.
Now calculating the current draw:
current draw = capacity / play time
capacity = 2160 (96% of nominal capacity)
140mA for MP3@128k
150mA for OGG@Q6
My patch will reduce current draw by about 50mA in both cases. In terms of play time this makes
24 hours for MP3@128k, but only
21.6 hours for OGG@Q6.
So the difference is now 2.4 hours. In other words: the lower the overall power consumption, the higher the difference in play time between different codecs!
Your 6 hours with OGG@Q6 will probably turn out to be 9 hours with the patch applied.