Making it ... and making it with 10+% range remaining with a family of 4+ are probably slightly different. I have no problem rolling in to a supercharger with 1 mile of range remaining but I try not to do that when I have someone with me let alone if I had kids along for the ride.
It's great that a 75D was able to make it the 185 miles and up the 1,300 ft elevation gain. It would help if you indicate what your starting range was, what your typical cruising speed was on the Interstates, what temp and fan the settings were (super hot and full fan, hot and med fan, average, off, etc.), and what your Wh/mi average was for the trip. Perhaps it was 250 miles starting range and 65-70 mph so 42 miles left would be ~16% but for some people that is below what they are comfortable having at their destination.
The 40 miles from Weston to Rt 19 and the 75 miles from Beckley to Wytheville are 70 mph zones on the Interstates. The section after Beckley has the larger hills to climb so tackling those at <70mph would be ideal while the relatively flat section after Weston could be driven at perhaps 70-75 mph without much loss of range.
A stop in Beckley for an early Dinner next to a J1772 charger would be an easy way to get some additional range to ease any stress. Maybe RedOctober wears gloves and a jacket and barely uses the heat while someone else cranks the heat. Those will be very different Wh/mi numbers for the same 185-mile trip. An S85 and an S75D look to have almost the same max range but I believe the 75D is slightly more efficient at driving due to the 2nd motor but forget if that has been tested anywhere.
Good luck either way to you, FrozenCanuck, but there are a good number of options even if the Weston-Beckley-Wytheville route is attempted so it is quite different than trying to make the same trip through an area that has zero charging options.