The HR measurement is not bad on the Apple Watch. I have a medical condition and I’m connected up to HR monitors of various types at various points of my hospital visits. The Apple Watch always matches them.
However it’s in epoxy and conductivity changes whether in plane of the carbon fibre or across it.
Happy to be corrected though. Here is the link, see table.
Carbon Fiber Properties-Heat Conductivity
The fork on the Expert is a Performance isn’t it? This is GRIP based (Performance and Rhythm) rather than FIT4 (Performance Elite and Factory). The FIT4 in the Elite/Factory does have some adjustment of the compression balance but not separate HSC and LSC like the 36. The Performance doesn’t...
I’m getting the impression that the level of assistance is set conservatively as the default on the SL to allay battery range fears. To keep up with the full fat riders could this not be turned up? You had range to spare after all.
700-800g is the normal Levo difference (Alu to m9 Carbon/alu rear triangle) but I’d forgotten that the SL is m11 and full Carbon. Maybe the difference is 1000g after all.
You might struggle on the forks and brakes. That would be functional (edit: as you say) rather than weight as the regular, not e-bike, 34 Rhythm isn’t that heavy. The cassette is heavy so you could save there or use the 10 speed SLX or XT setup that @Gary recommends. It’s light and I think fits...