I just punched your number into a calculator I use, upped yhe batch size to 6 US gallons, which is equivilant to 5 UK gallins and you should have an OG of 1.040-1 with a 75% efficiency.
however if I leave it at 5 US gallons it says 1.049-50.
however if I leave it at 5 US gallons it says 1.049-50.