Water changes won't slow your cycle as the water does not house the bulk of hte beneficial bacteria. The beneficial bacteria is housed on surfaces and predominantly in your filter. Doing wc's only dilutes the ammonia/nitrite so that its less toxic to your fish. THe beneficial bacteria will continue to grow as your fish produce waste. I would the levels as low as possible in order to reduce stress to your fish. If you want the tank cycled quickly, go fishless, add cycled media, and dose ammonia.