This is a very interesting articel of the effects of these pull-up resistors on the I2C signal.
http://dsscircuits.com/articles/effects-of-varying-i2c-pull-up-resistors.html
Good article. One thing to consider is that when the pullups get < 2.7K or maybe 2.2K, you'll
be exceeding the sink current specs for I2C devices, at least for 5V systems.