I'd say go for as much protein as you would have at your target weight, the reason being, your body will only use as much protein as it needs to function, build muscle, etc. and then as for the rest, most of it will be excreted through the urine. It won't kill your kidneys like some might claim unless you already have moderate to severe kidney dysfunction, but it will still essentially be a waste because it won't be absorbed. A little bit might get turned into glucose, but it's not a very efficient process so we can ignore that. For most people, 150-200g/day is probably plenty and in practice it's hard to get to that level because the food is just so darn filling. But for weight loss, that ain't a problem because you still end up eating less overall.