How close to the Agree can an Attain with a negative stem be.

Hi Cubers! 👋

I have been pondering upgrading my Merida Reacto 5000 from 2015 and and choosing between the C62 Agree SLT or Attain SLT.

I have signed up for Vätternrundan 2026, a 315km race and have at most done half ironman or 150km rides. The "race will be more of a group ride, but I think I will need all the comfort I can get.

But my question is if I feel like I need more aero gains, how close to the Agree can an Agree with the Agree stem (-6 degrees)? If they are similar enough I'm thinking of going with the Agree and "slamming" the stem downward or getting the negative stem should I get to the point where I feel capable of taking a more aggressive position.

Comparison between bikes: https://99spokes.com/en-EU/compare?bikes=cube-attain-c62-slt-2026;*z.53cm-700-700,cube-agree-c62-one-2026,merida-reacto-5000-2015