Wiz,
The only -8 Boeing is advertising is the 'bog standard' -8X, with a nominal range of 9300+NM. They may be planning a -8LR to go even further, chasing that elusive SYD-LHR non-stop, but it's not on their board. Besides, the weak sales of both the A340-500 and 777-200LR doesn't lend credit to the notion there's a market for 9000+ NM airliners worth chasing.
As per my previous, the -1000 will be lighter than the -8, seat around the same number of pax, and has less installed thrust. With the -1000 also having lower acquisition costs, makes it unlikely the -8 will be cheaper to operate.
Boeing 777X Airplane | Boeing Commercial Airplanes