The GT has Campy Record on it now, but it's the 10 spd bits (shifters and rear derailleur). The Paul brake calipers are set up for Campy levers. However, it's been a royal PITA getting a 10 spd Campy setup to work on my Wahoo Kickr. Campy 11 spd is more forgiving since that can run a Shimano 11 spd. HG cassette.
The Colnago has 8 spd Campy on it now (first year Ergopower from 1992) along with some vintage Mavic cranks that look really cool but could also be used as a small boat anchor. And the cog range for 8 spd Campy is somewhat limited and it would be nice to install something with a larger range.
The other part of the decision process is I really want a new road bike and that would pretty much replace the GT, so part of me doesn't really want to put effort/money into it.
I'll decide once the parts get to me. I do lean towards the Colnago since that bike is not likely to go anywhere and a conversion to 11 spd would mean it could go immediately onto the Kickr. The GT can run fenders so that is usually my bike for the occasional winter rides.