I dont think @velimir is much into cycling :) He has a nice and cool bike. I will upgrade to his level soon :)
Really is finding that perfect balance. Slower revs at higher power (it helps to have a power meter when you do this) and a lower heart rate will tend to burn your legs out much more quickly than a higher cadence at lower power and higher heart rate. How where exactly this balance is can be very different for different people. Also a lot depends upon how much load your heart can take before burning that out as well. Another huge piece is how far and how long you have to ride. You will find that your heart can take a long, sustained effort better than your legs in most cases, so I usually opt for a higher cadence, higher heart rate with a little less power. However, if I need a short burst of speed, I will go to that higher gear and let me cadence drop to increase the power, but only for as long as I need to. I ride between 5000 and 7500 miles a year out in Colorado where we have a few rather large hills and have found over time that a higher cadence works much better for letting me ride longer rides, especially when going uphill. So this is what i think