Thanks for all the comments.

@Andrew R Stewart
The seatpost height was a bit too high on the pic -- I had just switch saddle and there was a diff. in rail height, now it's back a bit lower.
I say "CX frame" but it's really an hybrid frame. There are eyelets for mudguards and for a rear rack so it's not racing only. Current position setup is for the city. I would make adjustments for touring.

I guess my question was really about double top tube effectiveness and/or diagonal tube effectiveness and it was answered : not really effective.

I'm going to balance the load. It's just that my partner has a knee problem and I must take more load than in the past. I mean, I enjoy the extra load because I can exercise more, it's just the wiggly frame that's a bit problematic and even unsafe when I need to steer a bit at higher speeds on descents for instance. Going to look into bigger tires and switch my front rim to a Rigida DP18 36h... we'll see how that goes.