A few years back a WG I visited regularly in London, agreed to let me film our encounter. We were engaged in a long session of 69 and she gave up sucking me after a minute or so, seeming to only enjoy my ministrations on her. After a few minutes she started moaning gutturally and contracting her muscles and pushing back on to my mouth and nose. When we were finally done, she told me she came really hard and thanked me. I thought, 'yeah right...you're just saying that to make me feel good about myself'.
Later on, when I looked at the playback, her face was worth watching from the end that the camera captured it! At first she was going on my tool..then her eyebrows rose, then she gave up sucking me and was focusing really hard on herself...eyes rolling in their sockets, biting her lips at times, sticking her tongue out at others...she was really very turned on! I still look at the video and get a kick out of turning her on like that :-)
I have since then tried a long session of oral on a few other WGs but have had a similar response only from 2-3. In fact one Russian WG I tried this on had a really tired and disgusted 'can we get this over with please' look when I looked up at her expecting kudos
So I expect this works only on some girls or if there is good chemistry.