I don't have the Bella, but I do have a 2007 low rise short. I believe that the Bella short and the low rise short are made with the same material. If I'm right, then the fabric of the Bella (and low rise) is significantly thinner than that of the T-short. It's really nice and luxurious feeling though.

I don't know how my low rise chamois compares to the Bella, but I do know that it is much nicer over long distances than the T-short. It's not as thick and puffy, but it is denser and holds up well when sat on for long periods.

I'm not a fan of the t-short, but I do really, really like my low rise. Because of this, I'd likely try the Bella if it weren't so long (I've got super short legs). My guess is that the Bella is a better bet for long rides - particularly if you are talking warm temps, too.