I've done many big mileage tours on the exact same model. I always aim to fill the tank at 150 miles. I can get 180 at a push but don't like to risk running out of fuel in a remote spot.
Always ride solo and find that its a brilliant bike to tour on. Magnetic tank bag and Kreiga 30 litre tail pack is all I need for 3 weeks travel around Europe.
An unladen STR is wonderful fun in the Alps, Pyrenees, Picos de Europa, NC 500 etc.