I'm trying to pick between the 56 and 58 frame size. My last fit put my saddle height a 805mm (with 175mm cranks). Jim at Lightcarbon has given me a seat post length of 380mm with a min insertion depth of 100mm (but 120mm preferred). This means:

Seat post: 260mm

Size 56: Seat tube C-T 518mm + 260mm = 778mm to 798mm (excluding saddle)

Size 58: Seat tube C-T 530mm + 260mm = 790mm to 810mm (excluding saddle)

I'd prefer the reach of a Size 56 but is this too much of a risk with the possibility of following the "smaller crank" trend?