When you say saddle bags, are you referring to the little bag under your seat? That won't hold much. Depending on the length of the randonneur, you might get away with it, but I'd check in that forum. But if you're touring, you need all the room you can get. Maybe you're thinking rack trunk vs. panniers? But that's not an either/or situation necessarily, although I find that with my current set up, the panniers ride too high and the rack trunk is too wide, so I can only use one or the other, but mine isn't a touring set up. You can do both, and if you're touring, assuming overnight stops and all the gear that implies, you'll probably want both, and probably front panniers, too, if you can, depending on the length of your tour. Some real touring folks will surely chime in, but I think the preference is to distribute some, but not half, of the weight to the front, making you still a little back-heavy, but not so front light that you have control issues. If I were in a situation where I could fit everything in the panniers or the rack trunk, I'd probably choose the panniers, as that would leave the rack open for other uses, although I would expect you'd be more aerodynamic with just a rack trunk and no panniers, so it may depend on your preference.