The fact that you stated that "it just dies, no sputtering" indicates electrical. Typically when a bike runs out of fuel, it rarely just quits. There is usually some degree of sputtering. Doesn't hurt to check the fuel system though. Hope it's as simple as that.
For the electrial end, I'd try isolating the electrical items that would cause the engine to quit. Side stand switch, kill switch, ignition switch. For the sidestand switch, you would jumper the plug that feeds the switch. Some switches are not easy to jumper.
Question, have you disconnected your throttle position sensor. Hate ranting on this but I had a problem similar to yours where my engine would cut out suddenly kind of like hitting the rev limiter but in the lower rpm range. It was the switch. By disconnecting it, the problem disappeared. Food for thought.
