the OTR won't be a huge gain, i'd only do that if you want less induction noise or are going for every last pony with bolt ons.
without going for a stallie then you'd be limited to a very mild cam grind, which IMO is a waste of your dollars, you won't gain much for your $$$. If you have a talk to a quality tranny shop you will be surprised at how well a smallish tight stallie will drive on the road, the newer lock up types will drive really sedately until you stand on it then they'll flash up to get you moving. That being said get rid of the 3.07 diff gears first with either 3.7 or 3.9 (keep in mind that 3.9 will have you revving pretty good in a A4 so if you do loads of highway keep in sedate in the gears) then see of that satisfies you for the time being.
if you do decide that isn't enough, i'd be looking into a stallie before cam, you will be too limited on how far you can go with a cam.