I've recently played around with acoustic treatment for a room myself, although I went for full height corner absorbers. I'll get around to writing up the experience and measurements when I finish playing and my trials with conversion of some speakers to active (both multi-year projects as I'm easily distracted).
I suggest the following link for modelling different absorption options:
You will probably need a reference like Bob Gold's absorption coefficient information:
For myself, I found some 22kg/m3 "fluffy" style batts (R2.5HD Wall Batts for the record) that I used to fill each of my 4 corners in a 430x580 triangle shape. The different sizes for the edges were to accomodate the windows and doors in the room and as it happened made for good use of a standard size batt, rather than any acoustic magic. The general rule is the more depth the better for absorbing bass frequencies. With only 3 of 4 corners filled to date I have taken T60 from over 1000ms to under 250ms which was a major part of what I wanted to address.
From my general reading, on the question of high density vs low density, it's a matter of what depth of absorption you intend to have. High density is better for lesser depths while if you can get over 600mm then less density becomes preferred (all depending on which source you read, but that was my ultimate determination). I went for the middle ground option, in a "superchunk" style arrangement.
You're probably aware already but there is limited measured data out there. A search on "superchunk" bass traps will get you some measurements, but not a lot, and a significant amount of debate over the best way to make one and the best materials and whether commercial options are a better use of your time and money.
I don't have them to hand, but if you want any measurements I've done with corner traps let me know via a message and I'll see what I've got. I'm not entirely sure how much use it'll be as i didn't do any comparitive measures between different styles of fibreglass, but treated vs untreated room. And none of the calculators I have found do modelling for corner traps, just absorbers mounted on walls from which you have to extrapolate results.
I plan to mount a 100mm deep panel on my rear wall for more trapping, and measure for a panel at first reflection points in the future, but it may be a while. I believe that some others have been purchasing and experimenting with polyester based panels so you might get some better information from them on higher density panels.