I also note that the Plus is stated to have a noise Level of 0.5 sone and 81CFM, 900-2000RPM (no noise level is given for the Plus II but the CFM & RPM are the same) whilst the TT2 says 0.3 sone and 54CFM, 1000-2000RPM. The TT2, Xtreme Plus and Xtreme 5870 are all rated for 250W and I find it hard to understand how the TT2 can do this with 54CFM, whilst the other two need 81CFM to do it (which must surely be noisier)?
In my humble opinion, AC just made some odd adds: each 92mm PWM fan accounts for 27 cfm and 0,16 sone (and the first figure is given at maximum speed, while the latter is with reference to the lower one).
So 2 fans give 54cfm and 0,3 sone (TT II), and 3 fans give 81cfm and 0,5 sone (XP II).
What do you think?