The easiest answer is to do the posted limit. Sounds dorky, maybe not as much fun as you would like, but a whole lot cheaper than donating the state general fund. As for out of state plates, never paid attention to it until the time of the stop. The state the vehicle was from just didn't matter to me, the infraction did. And the state never made an impact on whether I cited or not, the infraction did.
Now I have been through Marion county, where the rally will be, numerous times. The SO down there has a fairly large (for the area) traffic unit. According to their web site they have 9 units, motors and cars for traffic enforcement. Also says they are self funded, as in their budget comes from the money generated by their cites. This takes us back to the first sentence, if you are at or very near the posted limit and you see one of them or a trooper etc, there is not moment of panic or anything, just wave and motor on secure in the knowledge you are not doing anything to get their attention.
As for the jurisdiction between Salem and Eugene that was notorious for the freeway enforcement, that was Coburg. My understanding is that they have been talked about their enforcement activities. I used to see them all the time down there on the freeway. Since then, I have not seen them at all.
As for OSP, well, they have a whopping 300 some troopers for the entire state. Yes, I would imagine maybe more are in the valley area along I-5 than in eastern Oregon, but they are also the sole enforcement in some areas at times, so I don't know what their deployment is like. Keep in mind though that they also run fish and game trucks around too and they are just troopers assigned to wildlife enforcement but that does not mean they can't stop you just as easily. And they are a touch harder to see, most folks just aren't on the look out for dark blue trucks.
Still boils down to if you do the limit, you will not have any problems and enjoy your visit.
Oh and one other thing about Oregon, careful, Oregon law actually says no standing on your pegs. Not many LEO know about it, but some do. Oh and another thing, Oregon requires you to move over when you encounter a patrol car on the side of road on a stop is with its lights on. If you can't move over, to give a buffer of one lane, then you are to slow and move as far away as you can in your lane. This normally requires moving left if the patrol car is on the right shoulder.
See you at the rally, have a great, safe time!!