Thanks for all the comments so far. I guess I should have mentioned these would go on a 2019 Roubaix Comp so already have the futureshock and CGR seatpost. One thing I've found out is that the futureshock is great for bad chipseal and general rough surfaces but for potholes etc, it can actually be a detriment as there is no rebound damping so it can be worse than not having it at all. I know the new futureshock has damping but mine does not. After trying all 3 springs, I've gone to running it with no spring at all.

I'm currently running the GP5000's tubeless and will do the same with the new tires. I'm tempted to try and see if the 40mm Pirellis will fit but the GP-5000 AS in 35 is safer.