I bought the new C8 to try the extended range of the 800 chip. I have a 2800 sq ft house and a detached garage 25 ft from the house. The exterior is stucco with wire mesh. The C8 has a nice high central spot on the second floor. The C8 and previous C7 have had no issues with Zwave devices in the house. The C7 would not control garage devices. With the C8 I can find all the garage devices. They all are direct routed at 100 kbps or 1 hop. All of my switches are Zwave 700. I can report that the garage devices are prone to missing commands. Single commands or scene commands. I waited a week for my Zwave mesh to form for a week before I report this. With the direct routing or 1 hop I expected to report better results but this is not the case. I will give it a little more time before returning to a 2 hub solution.
Z-wave LR has not been implemented yet for the c8, so essentially range is the same as the 700 (but better because of the external antennas). Also for LR you must use LR devices (only a few are out at the moment) Given its a detached garage and range, I would do the 2 hub solution.
My C8 was reaching my detached garage pretty good after the migration. Probably go enough to leave it, but I moved my old C7 to the garage for all those devices and set up hub mesh. Moved a couple automations over to the C7 in the garage too just to spread the load out some.