The 8GB are more money, and often available because of this where the 4GB seem to be the ones everyone wants. I chose the 8GB partly for this reason.
I also coupled this with a 256GB High Endurance Sandisk micro SD card, mine has a v30 standard on it and it seems “pretty fast”. Had this card a for few years, stole it from my Devterm, there are faster high endurance cards out now, look for at least v30 and A2, v60 A2 would be better if the interface can handle moving data that fast.
Bigger cards have better endurance, you will be spreading the writes over a larger area so they last longer, and they don’t cost a huge amount over a good 64 or 128 card. Just my opinion.