H50, H70, CoolIT ALC series (and others), they are all "0" maintenance because they are "enclosed watercooling solutions".
1st. H50 and H70 have "about" the same performance, so if the difference in cash between the two is an issue for u then go for the H50 or the CoolIT ECO ALC. I myself use the CoolIT ECO ALC and its doing great at 4.01GHz, with tweaked voltages, it aint going over 76 C, at full load, after 8 hours (using push/pull fan configuration).
2nd. Why do u want a 4.2GHz overclock ? With your setup and for Civilization V, Napoleon Total War, FSX and torrents u really dont need to push for that extra 200MHz. A cool and stable 4.0GHz overclock is better at this point, if u ask me.
3rd. I, personally, rather not have to deal with a huge and heavy aircooler when there are so many other options with the enclosed watercooling solutions on the market. I cant say for sure, 100%, that it will fit (any of the air coolers) since u havent told us your case yet, but i tend to think it wont be a problem. Again, im not 100% sure.
4th. The applied thermal paste, the sitting of the cooling solution (be it air or water) and the way you tweak your BIOS settings are all very important, dont neglect any of them.