yo BB...
you are correct...I have completed runs of Action (1-100), Batman (1-100 and 1-103), Detective (27-101)...just completed the Timely MMC 2-92 (with a marvel 1 as good measure) and I am 9 books from finishing Captain America 1-75....in each case, I have completed the runs in 1 year or less....having said that, I have been collecting WW 1-84 for almost 2 years and still need 1 issue!!!! never seen it for sale....and, I did just start Sensations 3 months ago, and have about 70 of the 106 issues or so...but, there are at least 15 Sens issues that I know NOT where a copy is for sale (unlike the Batmans or Detective or Caps, etc)...
so, by comparison, the runs are much tougher, at least for me
rick