One, the mids on the 846 are more forward than the w60 but I would never say brighter, thinner or harsher. The 846's greatest strength next to the amazing sub base is the mids to me. How you described the mids on the W60 is how I would would describe the 846. It is the famous Shure house sound. However if more forward mids are not your cup of tea the W60 is the better choice.
Two, as I said in my comparison, even at high volumes the 846 is never shill, piercing or fatiguing. It was the sizzle of the W60 that was the problem.
Three, now here the W60 might be the better choice. With female vocalists I found the W60 to be a better IEM. I only listened a year ago for comparison purposes to one Adele song. I do not like female vocalists or even male falsettos so take my opinion here with a grain of salt.
Four, I would say the SE846 but here again take my opinion with a grain of salt.
If you read my review two issues with the W60 are also problematic. One, the build quality of the W60 is quiet frankly appalling and two, the tip size and insertion depth is very finicky to achieve the proper sound. However, I assume once you find the right tip depth this problem goes away.
As you read in my earlier review, while I prefer the SE846, the W60 is quite a good IEM and my preference for the SE846 was mostly governed by my genre os music.