I haven't opened my Iron Man Omnibus yet so I can't comment on the quality of THAT paper, but I am currently reading the Uncanny X-Men Omnibus and recently re-read the Lee/Ditko ASM Omni, both of which have very thick paper. Both of those volumes look HUGE compared to my other Omni's (of course the ASM volume is 4 MM's and then some) but I think thinner paper is a better option for Omniboo's to reduce their size. Also, when the pages are too thick I feel like I'm opening 2 pages at once and keep double checking to make sure I didn't skip a page!

Speaking of paper size and X-Men, those MM's look weird on my shelf. The 1st 2 original X-Men MM's are only as thick as a MPE and then Vol 6 is nearly as big as the first two combined! I wish I'd replaced those first 2 volumes with the Omnibus- especially since I don't have Vol 3, but too late now I guess