I recently switched my Maven JDK on my Mac from version 6 to 7 for a project at university. Later, when I built a fairly big Java 6 project with Maven for work, I noticed that it took considerably longer than in the last days. That is why I performed a little benchmark on this big project, and the results are striking.
Maven Build using JDK 6
Java version: 1.6.0_65, vendor: Apple Inc.
Total time: 1:25.398s
Final Memory: 66M/123M
Maven Build using JDK 7
Java version: 1.7.0_45, vendor: Oracle Corporation
Total time: 2:59.364s
Final Memory: 198M/673M
The build took more than double the time when using JDK 7, compared to using JDK 6. In addition, it consumed much more memory. Needless to say, I switched back to JDK 6 for building Java 6 projects on my Mac.