Save / Load will be fully available in the firs RC.
When exporting terrains to other applications you need to know how those applications import the data - there are multiple possibilities and World Creator supports them all. For example: 8 bit, 16 bit, 32 bit, little endian, big endian, normalizes, non normalized. We will do some videos on how o export properly into Unreal and Unity but it works as it has been done several times through users of our community.
The support got a bit slow right now since we are close to release - anyways, 3 days is not that much for a small team.
Yes, GPU generation depends on the driver you have installed. If it is buggy, it might lead to different results - that is why driver updates usually solve such issues.
We are going to upload new videos for the Standalone version only this week since the first RC is coming this week for all BETA testers. Those videos will show how to use World Creator.
Thank you and kind regards,