HI greggmacc, and welcome! Can't wait to see pics of your lovely new acquisitions; congratulations!
Speaking as another foreign Thorn owner ('Merkin in my case), I can surely empathize with the high cost of shipping and customs duties and conversion fees. Together, mine added nearly USD$1000 to the cost of my Sherpa.
As to rack selection, based on my experience, I can state with some confidence aluminum racks are fine for lighter loads and smoother roads and will last indefinitely in that service. However, I have broken four rear aluminum racks under heavy touring loads on rough roads...oddly enough, at the same point; the intersection of the last strut and the racktop. I would have figured the lower mounting eye to go first. I have yet to break a tubular steel rack, no matter the road or load, and it is not unusual for me to travel off-road for extended distances with an all-up loaded bike weight exceeding 50kg and my 78kg atop that. I have so far had great success with the Thorn Low-Loader Mk V front pannier racks and a Surly Nice Rack Rear. I have not had good luck with the Surly Nice Rack Front, as I found it to be entirely too flexible and sway-prone laterally. I do, however, seem to be alone in that experience as others simply love theirs. A search of the forum posts will find my comments on each in greater depth.
In choosing the Surly rear, I was put off the Tubus' by some online reports I read of fractures caused by parked bicycles falling over, and those failures not being covered by warranty. I have seen photos on the 'Net of broken Tubus racks, but I suspect they are notable because they -- like Rohloff hub failures -- occur so rarely. Frankly, any rack can and will fail given enough use and abuse, and the same holds true for nearly any component in expedition use. I do prefer the closed loop "return" at the front of the Surly and often use it as a handle for rotating and repositioning the loaded or unloaded bicycle when I am off it. I also like Surly's use of tubular stainless steel for the support and extension struts, as opposed to Tubus' solid aluminum rod, though I have never heard of a Tubus failure there. I don't think you'd go a bit wrong with a Tubus. If you like to place your load crosswise to the rack, you may wish to avoid the Logo, as it has a narrow platform, but it does have the advantage of a nicely closed front loop to the top deck and an entire secondary mounting rail to carry your bags both lower and farther to the rear.
I have come to firmly believe that external cinch straps greatly reduce the risk of breakage for mounting hooks and rack alike, and make the ride much quieter, all as a result of damping second-order vibrations. Going through a pothole with cinch straps results in only one "WHAM!" where otherwise you get the initial impact that lofts the bags and their contents and at least one more impact when the whole of the bags and contents settles down on the rack with force. Repeat often enough, and it isn't hard to see why breakage occurs and the wisdom of trying to minimize or damp the second-order vibrations and impacts. If nothing else, it is worth it to have a quiet(er) ride.
As for heel clearance, don't forget if you settle on Ortlieb bags, there is considerable adjustment possible in terms of hook location, and a bag can also be canted rearward at the bottom or even angled (with the later QL-2 mounting system). Bags by other manufacturers usually include some means for adjustment as well.
Best,
Dan.
