Hi Scubabrandon.
I was at Martha's Sat/Sun June 24-25, certifying 8 divers, so needless to say, I don't know the bottom temps! However, the top thermocline was quite pleasant. Surface temp was about 83-84. Thermocline was around 25 feet and the temp dipped into the mid to low 70s. It actually felt great as we got kinda warm diving shallow since some us were still bundled up in our hoods and vests. There was another temp change around 30 feet as well (and, of course, temp changes deeper than that too). Heard rumors that the bottom temps (55') are still in the high 40s-50s, but I cannot personally verify that. Viz was pretty good too... averaging 15-20 feet in the top 'cline. Most students were in 3mm 2-pieces suits and no one was cold and some even complained of being "hot" while diving. My DM stayed in a 3mm shorty and was very comfortable. Again, these were fairly shallow dives as our max depth was 35 feet.
Hope this helps and I hope the conditions hold. I've been out there almost every weekend since May and the viz has consistenly been at least 15 feet, with early morning viz in the 20ft range. You should have nice dives around the crusher/shaker houses. Lots of baby brim hanging out in the grasses too!