I think the pixie cut looks really good on you. I can understand getting bored though, and am wondering about changing the shape and/or even the colour - just for a change of pace.
The one thing I notice is that the pixie really makes your eyes stand out!
The bob looks beautiful on you too - and in terms of growing hair - mine grows like crazy, and I have to echo Mo on this one - I think it's because there's a good amount of healthy fats in my diet. Fish, olive oil, avocadoes, nuts and the like. I've never tried a hair supplement, so can't say whether they make a difference or not. My hair grows almost too fast.
Having said that, I recently got a haircut that I don't like, and was researching around to find out how long it might take to grow out some layers that I really didn't want - and it turns out that on average, hair grows about half an inch per month. So, if you were wondering how long it would take to get to the 'chin length bob' length - you could just measure where your hair is now, and the difference between the two to get an approximate idea of how long it would take to grow it out to the length you're considering.
And again, to potentially speed up the process, eat more fat in your diet. This doesn't mean blowing your diet or anything, just that fats are good for your hair, nails, brain and so on. Think: salmon, avocado, walnut oil, olive oil, that kind of thing. Measured portions to be sure, but I eat these kinds of things on a regular basis and my hair grows faster than I can keep up with sometimes (I have bangs and it drives me nuts that I have to go and get them trimmed practically every three weeks). I don't think you need to buy supplements. Your hair will grow approximately 1/2" per month on average, and if you up the fats in your diet, it'll probably grow a lot more/faster than that.
I would either change up the pixie (shape/style) or consider a colour change just to alleviate the boredom factor, or as you said - consider growing it out to a chin-length bob again. Both look very good on you, but I have a slight preference for the pixie because of the way it highlights your beautiful blue eyes. Try flipping between your pixie pic and your bob pic, and see if you can notice the difference in terms of just how flattering the pixie is in terms of making your eyes stand out. Just some food for thought.