I just think about your case again. If your current pending H1 extension is approved beyond the 6 year limit due to USCIS mistake (sometimes they may not realize your has reaches the 6 year limit and thus approve your case), you may just stay in US and continue to work. Then, continue to extend your H1 when your PERM pending > one year or I-140 approval. Then, when your PD is current, you may just go to China to get the H1 visa to come back before you file I-485. Thus, all your status record will be re-counted from the date of your last entry and thus, your I-485 will not be affected.
Of course, it your current pedning is denied, you may have to leave US for one year to get a new 6 year term, or get another kind of visa to come back as we have discussed.