Go to a forum that specializes in your bike and see what people are using. Note that a 140 mikuni jet isn't the same size as a 140 dynojet jet. There are charts online to help you with that.
Dynojet kits work fine but you pay $100 for $20 worth of parts. The other $80 is for the time they spent figuring out what range of jets will support what mods. I'm not familiar with the daves mod, but I suspect it's to correct the lean condition all factory carbs are set at to improve cold idle and warm up times. If you're just putting on a pipe, I'd personally start with one size up on main jets and maybe shim the needle, run it and see where it's at. Jets are cheap and since you only have 1 carb on an xr, it will be very cheap, but if you are going to just buy jets, hit a forum dedicated to your bike and soak up some more specialized advice.