I have had a similar situation. I have both Robert Beckman Panniers (Bruce's original "Pannier Partner" and they share a lot of the same setup design as Bruce's) that are made specifically for Bruce Gordon racks for my old Robert Beckman Sakkit bike (the original adventure touring bike). Absolutely love the setup and it is my preferred overall if the road is rough or off-pavement and/or it is to be dry during the tour.
However, i bought my Co-Motion Americano use (has disc brakes) and it came with Tubus racks and Ortlieb panniers. This setup is my preferred if my route is on good roads and/or inclement weather is reasonably possible.
Pros/cons of each. Gordon/Beckman packs are very well built and have few parts to break. They have absolutely the best system for staying securely on the bike regardless of the terrain and are pretty easy to get on/off. However, not waterproof without rain covers or drybags and are a little small for me. I have multiple sets of different sizes but even the tandem set is a bit tight at times. Definitely heavier than Ortlieb but way lighter than Arkel (they are HEAVY). Not too many ways to compartmentalize the gear as they only have a couple of sections per pannier. I am guessing the Beckman packs hold up a little better than in rough terrain (brushes, scrapes, etc.) compared to Ortlieb.
The Ortliebs are lightweight and waterproof. Very easy to take on/off. Lots of options you can add to the packs, i.e. small outer pockets, medium outer pockets, mesh bags, water bottle cages, etc. so you can customize for each tour's needs and to assist with organization. I really like how I do not need to get a much larger pannier when I can just add a pocket. The downside is the mounting system is not as secure. It rattles a little, the clips can come off (be sure to super glue them on once you got everything adjusted right), the mounting can break occasionally (carry a couple of clips and a rack guide), and parts are quite expensive for what it is at times. Compared to the Beckman packs, they just are not as nearly as well constructed. However, they are good packs so you are comparing an older Honda to new Chevrolet. Both are good but one is a older but a tad more reliable and one has better features but breaks a tad more often.
Overall, either system is OK. However, since you have a new bike, I would just buy a Tubus rack (very good) or Old Mountain rack and see if the Gordon packs can work (depends on what generation of Gordon packs you have). If the Gordon packs REQUIRE a Gordon rack (like my Beckman), would some spacers work (buy them at ACE Hardware) and see if you can push the rack away from the fork mount.
Since you probably won't be doing too much off-pavement touring on 520, I would lean toward the Ortleb and sell the Gordons to get some of your money back. If you had bought a Co-Motion Divide and wanted to ride on gravel quite a bit, I would maybe rethink this a little.
Best, John
