I am at 1.3.20 drone firmware and have no problems. This firmware version is still current on the DJI download website. I was at 1.4 and had some slight drift however, I believe this can be resolved by downgrading and then re-applying 1.4. Once 1.4 is reloaded perform a cold IMU calibration. You can stick your drone in the fridge for 5-10 min (while it is powered down). Pull it out, turn it on and then perform the IMU calibration on a dead level surface. Use a spirit level to find your surface.
If you go to 1.5 or higher you will not be able to downgrade below 1.5. You will essentially be on the "New System" which includes a performance downgrade (acceleration and speed) to improve battery reliability. Furthermore being part of the "New System" means that GEO fencing UNLOCK will be enforced on your drone.
If you are in a YELLOW area, your drone may not activate and fly in that zone without requesting a temporary UNLOCK authorisation from the DJI website which includes supplying your personal details and credit card info.
My RC is at 1.5 which was upgraded by the DJI GO App. I have had no issues using the RC at 1.5 with drone firmware at 1.3.20 or 1.4.
You make the informed choice. Good Luck.
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PS. It would not hurt to backup your current DJI GO App in iTunes should you be compelled to go back to an earlier version of the app in the future.