This is actually pretty normal, on stock settings mine also only reaches 1071 max boost. Nvidia state that every GTX680 will have a minimum Boost Clock of 1058MHz but as has been the case in the past each card will vary. GPU boost on stock settings will increase the clock speed of the card in 13MHz increments between 1058 and 1110MHz, so your boost clock on stock settings will be 1058, 1071, 1084, 1097 or 1110MHz. I saw on here that Darren's card can reach 1137 on stock settings which is the highest I've seen and exceeds Nvidia's theoretical numbers but 1110 seems pretty common. Also, try and keep your temps below 70, above this point GPU boost will start to throttle your clocks and voltage, but may also do this as a result of exceeding any set power target, so increasing power target may help but only once you have temps under control.