No offense, but if you start doing whiskey/mashing again I'd strongly suggest finding a different enzyme supplier.
A good supplier should supply you with the graphs and efficiency charts so that you can see where they are most effective, and where they actually begin to denature. Most enzymes have a point where they temporaraly denature and permanantly denature. Meaning if they just start to denature at 180, but are 100% efficient (at the right pH) you'll likely be just fine mashing at 180.
Also by the time the pH crashes, your alpha should be 100% done doing it's job and it's time for the slower gluc enzymes to start waking up. I think my second enzymes don't hit peak efficiency til around pH 4.2 which is perfect for once the fermentation is rolling along.
If your enzyme supplier just states "150 degrees" I'd look elsewhere because enzymes may be (relatively) cheap, they are the backbone of your mashing operations.