I'd guess 200k miles would be my limit for the rubber lines and lifetime for the steel lines. But I don't live in areas that salt the roads, ymmv. At 115k mi now and they are fine.
As an aside, the stainless braided lines aren't buying anything other than steel braids and they look better. Its a hotly debated topic. You gotta be lapping a high HP car on a road coarse with high temp pads and even then I question anyone that says they can feel the lines expand. My calipers bowed, felt that and there was clear evidence but the rubber brake lines are hydraulic lines.
FACT: braided stainless steel lines are not buying anything other than they look cool. And I will admit that the looks just matter to me...which is fundamentally the reason I am using them (instead of some kind of racing performance). They might be a little tougher and more robust than plastic but these lines are not going to change the performance of the truck (in any conditions).
I actually have some notes on this brake rebuild and have been chatting with Atlantic British as I bought their product from Tera Firma. That may be worth a separate thread someday (this whole rebuild project is still ongoing and includes the calipers) but there are a number of downsides with this aftermarket gear which requires some fabrication to make up for the shortfalls - so folks should be aware before diving in. Furthermore, the Tera Firma product are for 2+inch lifts...which I don't have and therefore we have some "extra" break line or slack to account for in the wheel wells (not a big deal but it is critical to keep things clean and very organized in those wheel-wells with everything going on...particularly on the highway at speed or while off-roading).
200,000 miles life-span for either plastic or regular steel lines on these trucks seems reasonable but as you noted: depends upon conditions, particularly salting. As for me, I have done several anti-corrosion campaigns over the years and those seem to have helped quite a bit (at least it seems so).
