Both points are true, but in my mind, the discounted models today are already only the base models (8/256 and 8/512). You almost never get discounts on BTO models, again except occasionally at B&H Photo. So it doesn't really matter.
If you need a BTO configuration, then you generally have to buy from Apple anyways, and there's no discount. So even more so, if you're in this situation, you might as well wait until M3 released.
If you're ok with standard base configs, I still think you should wait when we're this close (again, assuming you can). Even with the discounts, I think these will still remain post-M3 launch.