When building with SunStudio12.3 I'm seeing a warning that -KPIC has been deprecated and needs to be changed to -xcode=pic32.
I'm seeing ~3% decrease in G1 pause times with this change along with moving to Solaris Studio 12.3.

Stock G1
1602 collections, total time of 4.21628 average pause of: 0.002626966

Using 12.3 along with -xcode=pic32
1605 collections, total time of 4.09735 average pause of: 0.002552866

~3% gain.
More data:

T4-1
JDK8-b48 (Both unmodified and modified)
JVM Flags: -d64 -Xms64m -Xmx256m -XX:+UseG1GC -XX:InitiatingHeapOccupancyPercent=20 -XX:+PrintGC -XX:+PrintGCDetails -XX:+PrintGCTimeStamps

I ran GCBasher 5 times, with a runtime of 900000ms with the G1 collected and grepped the logs looking for "GC pause" and added the times up. I then averaged the times (time/# of pauses) to get the average pause time. The results are as follows:

Stock G1:
4820 collections, total time of 12.315 seconds, average pause of: 0.002554979

Using Solaris Studio 12.3 along with -xcode=pic32
4824 collections, total time of 12.0829 seconds, average pause of: 0.002504747