Geofelt had good suggestions, it may be why others aren't chiming in. For intel cpu's there's a temp guide that gives some indication you might find helpful.
http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html
There really isn't an 'ideal temp' to keep it at, there's more of a temperature range. Many things factor into the variables, ambient room temps, which cooler you're using, what load (ie web browsing, gaming, prime95, full fpu/avx load etc). For most basic use I'd be concerned at around 75-80c and that's under gaming loads. Not concerned enough to yank the plug out of the wall like everything will melt down but hot enough I'd consider checking if dust has collected in the cooler, check cooler mount etc if the ambient room temps aren't 30c+ that would explain the heat.
Personally I prefer a cpu to top out no more than 80-85c under heavy load like prime95 (version is important, read the intel thermal guide link). That should be a worst case scenario, below thermal throttling and normal activities like general use, gaming etc shouldn't push the cpu harder than a stress test like prime so temps will generally stay around 70-75c or less.
For the 1080ti fe (founders edition) anandtech's testing shows they topped out at 84c which is the thermal throttle point for the card. Around 80c sounds about right, give or take a couple degrees. Other editions of the card from 3rd parties with varying coolers may achieve slightly different results.
http://www.anandtech.com/show/11180/the-nvidia-geforce-gtx-1080-ti-review/16
Tom's Hardware's testing got similar results.
http://www.tomshardware.com/reviews/nvidia-geforce-gtx-1080-ti,4972-7.html