BY SGR due you mean specific ground range? On the presumption that you want to know how much fuel you will burn. Our training manual says to allow a 10% increase in burn when holding with flaps 1. Worst case that all the leading edges are out and you are limited to 230 knots and 20,000 feet. The only figures available to fly at those speeds are holding speeds and fuel flows and for 800 and classic that speed equates to a max landing weight figure of approx 1200 kg per engine, 2400 total. Make that 2640 allowing for the 10% increase with flaps out, 230 ias is about 310 tas so 2640 divided by 310 implies that you burn 8.5 kg per nm. The normal burn 2 engines is 6 kg per nm, 1 eng 7kg /nm (800) 8 kg per nm ( 300/400) and for interest 14000 cruise 2eng depressurised 8 kg/nm and 10,000 9 kg /nm. So if you have only the flight fuel for a diversion with 10% of that as variable plus fixed fuel reserves and approach fuel, you will be declaring a mayday as you will have eaten into your fixed reserves by the time you arrive at the diversion airfield if it is your decision to go.