TeslsCam writes at an approx sustained 4MB/sec (note Bytes).
Storage size is largely irrelevant (unless you like hoarding stale clips or need to leave the car on sentry without checking for several weeks). However the larger the media, the less frequently it will overwrite the media memory - it is these overwrites that will ultimately wear the memory out.
imho, from a price/reliability POV on SD cards, 128GB seems to be a good place to be.
On subject of reliability, an Endurance spec card if going for SD format or most types of SSD drives should be more tolerant of repeat overwrites.