Unfortunately, there seems to be a lot of opinion mixed in with a lot less fact.
WHY is 375 too small?
The author of one of those articles (manutius) says 1000g minimum and says his 90g is too small. Agreed. 90g is too small. I'm not entertaining that as an option. But there is a lot of room between 90g and 1000g.
http://www.**************.com/forum/library/puffers-in-focus/mbuforyou/
Another poster (RTR-mentor) says 400g - well, I'm providing about 450g of water (give or take) and an automated drip system. Filtration/water changes - check. I have absolute confidence in my ability to provide a pristine environment. I'm not new to keeping fish, internet boards, varying opinions, or puffers. In my opinion, the fish that best display personality are datnoids and puffers.
http://www.**************.com/forum/viewtopic.php?f=56&t=23704
Another poster (Pufferpuggirl) has an mbu is a tank that is CLEARLY too small (judging by the thickness of the glass in her pics) to house anything other than an adolescent mbu.
http://www.**************.com/forum/ug.php/v/User_Galleries/schismy007/BeeBoo+three+19Jan.jpg.html
Another poster (Li$a) had an mbu and planned a 450 as the permanent home. Unfortunately, her mbu died

http://www.**************.com/forum/viewtopic.php?f=56&t=22227
I'm just trying to accommodate the fish as best I can. I would prefer not to guesstimate or take someone's idea based on Kentucky windage. So, help me out here.