Alpha3,
I just added 2 JL f113s to my 2 channel system. They are very fast and so far they have been easy to blend in with my front speakers thanks to the use of the calabration mic and the LFE trim for low level bass. I am not finish setting them up yet but so far so good. I hope these are my last subs!
On the front wall of my system I have had the Aereal SW12 it is also very fast and I was happy with it till I heard the f113s. I also had the Rel Stadium III, I did not feel it was fast enough for 2 channel. I have found that the f113 is better than both and has much smaller foot print to boot. I did change to 2 sub for stereo this time though. I still have a Rel Statium III in the rear for HT use and will sell off the Aereal SW12 shortly. I will try the JL f113s with the HT system after I finish with the 2 channel setup.
My room is 20'X15'X8'.