Haha, did he have a 1250 for sale by any chance!
Either bike should have more than enough reserve electrical power to run all your heated gear, the cause of all your woes on the other thread were probably not just down to the load you placed on the bikes` system but a combination of age, wear`n`tear, weathering and general useage. GS alternators are an oft-replaced part, are they not? They don`t last forever, your heated gear is quite a load though and may have shortened the life of a middle-aged alternator. Who knows, impossible to tell, really.
It seems a bit bizarre to choose a bike on it`s alternator output but for what it`s worth the 1250 has 500W and the 1300 has 650W, the increase on the 1300 may have been necessary to power all the extra gubbins those bikes are saddled with such as ride height motors, radars, `leccy screens and gawd knows what else. Take those loads off the total and you`re probably left with a similar surplus electrical capacity to that of the 1250.
They do seem to have upped the load you can put on `all onboard accessory sockets` from 5A on the 1250 to 12A on a 13. That may help you hook up all your gear..
How is diagnostics on the 1200 going, have you been confident enough to connect the battery up yet!