Well, if you want my honest opinion on this...
Something I should've said before is that you should clean up your computer first. Get a can of air duster and go to town with the computer. 55C idling on a decent air cooler is a bad sign. If your temps don't improve that much, then replace the thermal paste. Both of these should lower your temps. Otherwise I don't see much of a point in getting something better. Lower temperatures doesn't really do much other than buy the part more life (on what amounts to what I think is 5+ years when going up to 80C under load).
In any case, do your own research. Use Google or whatever to look up reviews on those parts, then make your decision.
Ive done that and I also replaced my case entire fans and I think its more to do with the temp with my room which is hot in the 90s and I replaced the thermal paste with little changes but as you stated, I want to add more life to my cpu. In the morning my temps are at 30-40 in the afternoon though it runs in the 45-55. I want to switch to cooling but I don't want to take the chance of having a leak but as well I want to switch to another air cooler like the Phanteks PH-TC14PE_BK but I don't know if I have enough space. Even with my zalman 9700, I have about a in before it hits my side wall case fan and at the moment my ram fan is already hitting my cpu cooler