NovaBench is not very accurate, GeekBench do a much better job.
Anyway, Use 2+8 should be the best option. There is no need to use matched pair on a Intel Mac.
Also, the current OSX is very good to fully utilise the RAM, more RAM means more cache, which means a faster machine. Therefore, a single channel 8G config should run better than a dual channel 4G system. In my observation, the OS itself can easily use up 6G of RAM (if available). 8G is definitely a better option for Maverick.
Moreover, unless you are doing some very RAM intensive job. You should not able the see any real world performance difference between single and dual memory channel config (even though there may be 6-8% overall performance in benchmarks).