What are you going to do with the file you export? Upload to YouTube/social media or to have a file for archiving, or?
I did a test with 1 minute long timeline. If i export it to H.264 @Deleted User mbps it ends up being 11.2 GB. If i export to ProRes 422HQ the file is only 1.26 GB. Thats why i wonder why you aim to use a H.264 at those bitrates that create really huge files when there are other codecs that dont degrade the footage as much as H.264 does. H.264 is a lossy codec while ProRes is a visually losseless codec so if you want the ultimate quality H.264 is not as good as ProRes despite that the H.264 is ten times larger than the H.264 file. In short, bitrate alone is does not define highest quality.
For example:
Back in the day when DVD´s were a thing many people often wanted to export a H.264 file for the DVD since they considered H.264 to be best. But all DVD´s are always MPEG2 and if you bring in a H.264 file to author the DVD the H.264 file will always be re-encoded from H.264 to MPEG2. This means that you will loose quality, always. So sometimes one have to choose the best codec for the thing/s one need/want to do. There is no codec that does it all. It´s a workflow thing.
Btw, i got a crash here as well with Pr 25.0 with H.264 at 1600 Mbps, but the file was usable.
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