@YouFinished: The Chibaku Tensei is a glorified sealing technique, and has only ever been used as such. Pain even said that his mini version should be enough to CONTAIN naruto, but he could increase the size if anything occured, meaning that it was not ment to kill him.
The Jubi was also trapped inside a formation that was Chibaku Tensei induced, the moon, . You use the argument that because Kurohitsugi was not warping space-time noticably on the exterior at that moment then it was not doing it at all (Despite the fact we could not see inside at that time, for all we know Aizen was telling the truth, He only said it to make Ichigo's power all the more impressive. Hyperbole or not the feat is more impressive than anything I have seen Naruto do as of late), Well Chibaku Tensei was not used against naruto offensively (Only to capture him and contain his power) so he didnt "Tank" that attack since it was not used to attack him in the first place, there was nothing to tank.
His best feats of durability in Tailed Beast form could amount to Mountain level eventually butI would not use Chibaku Tensei as a durability feat since it was not used against naruto to inflict harm upon him. If pain wanted to kill him the entire attack on the village would have been counter-productive, which gives even more base the the fact that attack was not to harm or hurt naruto in any way, other than to immoblize and capture him. I personally would NOT use that as a durability feat since it was not used as an attack intended to inflict harm against him, but if life has taught me anything its that we all have different ideas and opinions and just have to respect them, because chances are I will not be able to turn people to my way of thing with one speach or post.
Bare in mind, I am not saying he is not Mountain level in his Tailed Beast forms, I am meerly saying that I would not use Chibaku Tensei as a measure of his durablilty.
As for the 8 Tails breaking out of Chibaku Tensei, Its really not all that impressive. Since the 8 Tails is equal in size to the 9 Tails it would have been bigger than the Sphere itself, and when it formed it only had one way to go and that was out. Besides the rocks were not compressed enough to make it solid (The cracks running all over the surface) so any sufficent amount Tailed Beast power released at the centre would have been enough to break out of it if the target was conscious when he/she was being trapped.
As for Ulquiorra's Lanza del Relampago in comparison to Las Noches. The size if Las Noches is not stated outright, but testimonies to its size were given many times, Like when Ichigo and his team were walking for hours and the Fortress never seemed to get closer, Nel said herself that it takes about three days to move from one side to the other. It is more than likely the biggest structure in the enitre verse, and its size is not far off, or could even equal that of the Seireitei. And Lanza del Relampago was calced at being Town+ in terms of destruction, which is not all that far off from mountain level so he is a good comparison for us to use.
Frankly until Naruto shows so new feats that could put him above Ichigo in his Dangai/FGT form, Ichigo destroys him and Luffy. I mean naruto has really only recently (by that I mean it has not been as long as the other 2) been a confirmed hypersonic character (I believe his sage mode was around mach 5-6), while the other 2 were hypersonic for years and even going up to hypersonic+. Ichigo's sword swings in his Dangai form were calced at mach 28, which is double if not triple what naruto is capiable of currently (I cant see him getting past the the low to mid teens (11-15 mach) in terms of speed with this new form, But I could always be wrong). And luffy was Hypersonic+ for a long time too before naruto was so they both out class him in speed. Frankly the only thing he really beats them in is sheer raw destructive power (and even that takes a few seconds to achieve).
Also breaking out of Kurohitsugi was not a strength feat, it was more a testimony to his spirit power, and the wave of his hand was him releasing copious amounts of it in order to "Crush" Kurohitsugi.
Like I said Ichigo wins until naruto shows something more impressive. I would say he could do it without the use of FGT, but it would be a much harder battle that way.