I have done this, it made pretty much identical power curves for both (slightly less midrange torque without, but not enough to pick it), it just used shitloads more fuel without the TVIS.

I would have thought that you would pick up the air speed due to the smaller butterly size for each cylinder, and hence do away with the need for the TVIS. couple this with some mild cams and you wouldn't notice the difference without it.