1L bike bottles

I’m a hobbyist rider, not a racer. But I have a four-hour event coming up in May (GFNY), and even 20-oz bottles have been about the biggest I can comfortably fit inside the compact frame in my 2021 Specialized Diverge. So bigger bottles are not an option in the front.

I posted THIS NEW THREAD asking for recommendations on rear hydration systems that mount behind the saddle, so I can put two large bottles back there. From what little I understand, I need a base mount, two cages, and two bottles.

Like many of you, my first priority is bottle retention, my second is largest bottle size, and my third is the overall bottle/mouthpiece quality and feel. But unfortunately, after reading 209 messages in this thread, I’m not real clear on which bottles/cages are most recommended for road and light/medium gravel in a case like mine.

Any input appreciated, either here or in the other thread. Thank you.