The Aprilia V4 gets terrible mileage (see also: Multistrada V4), so you'd need a 30 litre tank to compensate.
Keeping things somewhat on topic, have you tried the XR? I know you've got a thing about i4's, but I personally think you've been on the wrong ones. My ZX-14 and ZX-10R had faults, but a lack of character wasn't an issue with either bike (for very different reasons, though). Nobody says that about the XR, either, with most complaints centering on its revviness and general angry quality. The above test specifically rates the Versys because it's smooth and predictable, while the BMW is much more raw. It's got all the gadgets, all the power, all the handling, good wind protection, legroom for taller riders, Euro brand cachet, can munch miles, can do twisties.
Just a thought, anyway...