Short answer, I love the XS30's and don't regret the change at all.
I wanted duals, but not at the price of purchasing a second PC13. I got the PC13 at an incredible price new (before price increases, plus it received the a discount for repeat customer). I also received the updated Sledge amp under a warranty exchange from problems on the original Bash. Keep in mind that I never did get a chance to compare them side by side since I sold the PC13 about 2 months before I purchased the XS30's. Plus, I was swapping out equipment and purchased an antimode since adding the XS30's, which replaced the BFD that I used with the PC13. Although I was able to get both scenarios to have fairly flat response curve with REW, I have had lots of changed variables, so take my comments for what it's worth:
Regarding ultra low frequencies: I have a bad null even with the duals, but over all, the XS30's fill the room much better. I feel the ultra low pressure much more now, but there were times that I recall feeling the air (like wind) more with the PC13, even though it was across the room (different, but incredible). I couldn't ever tell if it was from the port or the pressurizing of the room?? I did have to put some heavy EQ with the PC13, as the lower frequencies were so much more pronounced due to my room gain.
30hz and up: No contest - I love the XS30's. It fills the room and just sounds powerful. I can't really add to this. I was never satisfied with the PC13. It may be because the PC13 is designed to be an all out ULF sub, where as the XS30's spare no compromise in the upper frequencies of the sub range. I think it is a combination of this and that I am now running duals.
I hope this helps.