If you're on H-1B and your I-94 is about to expire and you have the option of renewing it i.e.. you have not yet reached your 6 year limit, I would have my employer file for H-1B Extension. Once the H-1B Extension is approved, you will automatically receive a new I-94.
This is just so that you cover yourself in the worst case scenario (God forbid!) of your I-485 application having a problem. Technically speaking, if your I-485 is rejected, you can still continue to live in the country untill your 6 year H-1B clock expires but for that you need to ensure that there are no discontinuities on your H-1B. The EAD is filed on the basis of a pending I-485 and cannot be filed under any other circumstances.
Again, just trying to think from a worst case scenario, sincerely hope your I-485 is approved quickly.