You can upgrade the drivetrain to electronic any time. It is impossible to upgrade a rim frame to disc. If you like disc, I would get the disc bike. The rest are simply incremental upgrades.

I don't know what your current wheel situation is, but you mention having a Tarmac disc. So you have at least one set of disc wheels. If it was me, I'd get the Felt disc so have wheel compatibility between at least two of your bikes.

I'm no expert, but I have a 2019 IA16, and if I could change one thing it would be the rear rim brakes. Pretty weak stopping power.

I'd go with the 2017 because of di2. Upgrading to di2 is pricey even if you do it yourself. I'll never buy another non-di2 bike.

I have ridden both rim and disk brakes. The only time I've wished I had disc brakes has been in terribly cold, rainy weather, with very low visibility and lots of grit on the road. (December/Jan in WA state). All other times, rim brakes are more than sufficient for stopping power with any rim, aluminum or carbon. I weigh 210 pounds and love descending.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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Owner of older Felt IA1 rim brake with DI2 and 2020 Cervello PX with Disc. Love disc brakes, but if I was choosing between disc brakes and electronic shifting, I would choose electronic every time.