I would suggest taking a look on Flickr at some places you'll likely to visit and check the EXIF data to what is the standard length and shutter speeds (and also aperture).
I would say the 70-300G is a lovely lens and sharp wide open (well mine is!), but wide open is only f5.6 which might be an issue depending on light.
The Sigma 100-300/4 gets good reviews and so does the Sony 70-400G.
I have been tempted to swap my 70-300G for a 70-400G, but think with the size and weight of the 70300G being small enough to take to the park with the kids, I think a larger longer lens is an addition rather than a replacement.
Once you look at these larger and faster lenses, it all starts getting expensive, and I would say, you need to know what you need rather than ask what you need, otherwise you might make a few costly purchases that are not exactly meeting your requirements.
What zoom do you have at the moment? And when you had your beercan, did you find this a little short? did you find that you were struggling to get a decent shutter speed and needed faster glass?