Updated to MacOS 10.13.4 last night, and I'm noticing quite a difference in the way the internal fan is working. Before, you'd never hear it at all until it kicked in under a HEAVY load, then it would run at maximum until it reached some preset temp, and would suddenly fade out. Now, the fan speed ramps up and down slowly, much like a regular iMac does, through multiple speeds. From quiet whisper, to full on hair dryer, and everything in between. Performance, especially for GPU computations seems nicely improved (less throttling?). But I'd really like some method of telling it whether to "run silent", or "run fast" while I'm working.