My experience:
I submitted my I485 while I was in OPT. Four months later my employer submitted H1b petition for me with premium service and I got H1b status. Therefore, you are still in your OPT even after filing I485.
However, USCIS may not allow you to have two EADs at the same time (OPT and 485 EAD). You can apply for EAD within 4 months of your previous EAD expiration date.