is a 1200W psu overkill for 290x in cf?

yes and or no. depends on how many things you have crammed into your case?

your 290x's have a tdp of 290w. combined that is 580. spikes from high res gaming can make that 650-700.

Cooling loops, excessive fans, extra HDD's, etc all have an impact on total wattage and more importantly amperage per rail.

The short answer is: maybe.

The better answer is: here is the tool you need to find out for yourself. :)

http://www.extreme.outervision.com/psucalculatorlite.jsp

Has an very robust parts list even listing random and rare parts. wattage accuracy is on target.
 
is there a negative aspect to having more money in the bank than what bills require? :)

Having more wattage allows for more upgrade room later on. never forget that until something major changes, the only 2 parts that you can truly "future proof", are your case and your PSU. optical drives would be a close 3rd since that tech only gets updated once a decade at the moment.

Main thing is make sure you do your homework on the psu so that you are sure you have enough amps on the 12v rail for your future graphics card dealings you think you may plan for and etc. check reviews. do many people have the same problem? if so how was their rma exp? etc etc.