I know everyone will tell me I am an idiot who is going to ill myself, but I have a 1000ltr IBC in my van, and on accasion have forgot to turn off my water overnight and ended up with 950ltrs in it, I get on fine with it, although I am going to change to a 650ltr when I can afford it so I can get my race bike in the van.
Without baffles the tank doesn't really make too much of a problem, in fact it slows you down and pulls you back when you get a slosh on, never had a cornering problem, and you are only over weight when you go out in the morning if you have over filled it!!
Marc