Well, I think 1.42V is a little bit high considering that a normal operation load is recommended at 1.3V. However I have my 4790K OC ed at 5.2 Ghz, same specification as yours, by the way, at a voltage of 1.40. So not being able to reach 5.0 on 1.42v but able to reach 4.9 means that the silicon pick on your cpu was about "gold rated silicon".
Anyway, back to your topic on if you should back down- I would run LinX for 15 tests on 80% of your memory and see if the system is stable afterwards. If not, I think it is not a good plan to keep your cpu at that voltage.
Hope it helped.