Performance wise, warm (not too hot) cap vs cool cap is trivial, ... BUT ... their life will be shortened almost exponentially. Check this out
OSCON Cap Life vs Temp.
On that chart, that is Sanyo Oscon cap, one of the best in the world.
Those with purple label at second pic in Spawn-Inc's post above are Sanyo Oscon cap. So you can expect much more shorter life vs temperature for non branded or 2nd tier/lower quality cap compared to these top quality one.
Now, when those caps are getting "roasted", they will not die suddenly, instead their performance will degrade and affecting the power quality to the cpu "gradually". The geek/tech speak is their ESR (Equivalent Series Resistance) will getting higher from time to time, and will have impact the VCore delivered to CPU in a really bad way when they're getting near their end of life. Thats why older mobo that was heavily overclocked before for quite some time will never have the same VCore's quality as the new one.
If you're replacing your mobo say for every year, I think looking at above cap's life chart is not a big deal, but if the rig is planned to be a server running 24x7, and will be placed in the corner/closet with a so-so air circulation and will be forgotten for quite sometime, it is recommended to cool those caps by putting small sink on the inductor (black boxes) to dissipate their heat faster instead of radiating it's heat to the caps, or the easier way is by putting small fan blowing those area. Also sinking those inductor especially the rounded cap is not easy.
Other proof, click on my sig on "
Inductors are hotter than mosfets", you will see the inductor basically are toasting the surrounding caps. From that pic, those mosfets are not that hot compared to the inductors from that infra red readings. If you're running your rig on bench table, just touch those black boxes while on high load with your finger to see my point.
.