Cool experiment, @burtlo! And more accessible than 3D flying.
Your build reminded me that my first two multirotors were both plus+ configuration. On the big +8, I suspect that x-configuration wouldn’t have been any different. However, the original Blade mQX came set up for +4 out of the box. On a floaty brushed motor geared micro, the plus+ configuration was noticeably more stable than the x-configuration (which I tried a few months later).
A few months ago, I passed my Blade mQX (set up in X-configuration) on to @bicyclewrench, who may want to give plus+ configuration a try as well.