I once lost an entire marathon set because a cheap reader failed. These are decent, reliable budget picks.

• Lexar Professional 128GB CFexpress Type B
• Nikon EN-EL15c Battery

Caught your post a bit late but honestly the transition from SD to CFexpress is mostly about managing heat and sustained speeds. For a marathon you dont want the camera slowing down after 20 frames because the card is struggling to dump the buffer. The Z6 is fairly picky with some of the older XQD/CFexpress hybrids too. If you want something thats basically bulletproof for heavy action check these out:

• Delkin Devices 128GB BLACK CFexpress Type B
• It has a 1400MB/s minimum sustained write speed which is wild for the price and comes with a lifetime warranty.
• Sony MRW-G1 CFexpress Type B Card Reader
• This one is built like a tank and handles the heat better than the cheap plastic ones during long transfers.
• SmallRig EN-EL15c USB-C Rechargeable Camera Battery
• These are great because you can charge them directly with a phone charger or power bank if you forget your cradle. Take a look at sites like Alik Griffin or the Nikon Rumors compatibility charts. They do deep dives into how different cards handle the Z6 buffer in real-world tests. One thing to watch for is that some older XQD readers wont read CFexpress cards even though the slot looks identical. Stick to a dedicated Type B reader to avoid headaches on race day. Definitely update your firmware to the latest version too since it improved card stability a ton.

^ This. Also, unfortunately Lexar sustained speeds are often disappointing. I prefer ProGrade Digital 165GB CFexpress Type B Gold for its 1500MB/s minimum sustained write speed. Tech specs dont lie.