thats a mixed question as the THD is usually a result of interaction with a particular load-so it cant really be told unless you specify your phase leads/lags etc...
The IGBT units are the best at fitting the general specs. like 3rd order harmoinics which are common in audio stuff. but thats a vauge guess.
i would consider running my crown THD unit but its too valuble to me to start putting it on line level stuff. even though ive had it on my techrons 10ks but in a special enviroment.
you have to really measure your power phase in on idle and full load and calculate the shift necessary. I can come up with an awsome value at idle to advertise and impress you but it will be a trick..
if you run it on the battery it will be = to zero.