Cabelas usually doesn't run really great sales unless they have some in stock. The 1858s have mostly been backordered during this run of sales, which is probably why they discounted the 1860s but not the 1858s (usually they do them more or less in tandem). I notice that the base model 1858 is backordered 2-3 weeks right now. Those are usually pessimistic so let's say it's really 1-2 weeks. That's the soonest I'd expect a deep sale.
PS Yes, the 1860 is on sale and it's backordered months, but it was in stock when they lowered the price in the first place.