Yes, people are using the six-series E-flite motor (the 2000Kv verson). Not sure on what prop they're running tho. The website says what props to use with direct drive and gearboxes.. maybe you missed it.. here's the link. Look under the Specs portion.
http://www.horizonhobby.com/Products...rodID=EFLM2000
If you're talking about the park 400 specifically, I haven't heard much. Also, are you talking about the 400 inrunner or outrunner?