GCC 4.10 has been under development since the 4.9.0 release near the beginning of the year. However, at the GNU Tools Cauldron it was agreed upon that GCC 4.10 will most likely become GCC 5.0 upon its release in 2015. The GCC version scheme is also being shaken up for future releases. Years ago there was talk of GCC 5.0 being modular and more like LLVM but to date there's no "killer features" of GCC 5.0 at this point in its SVN code-base.
Anyhow, for seeing if the performance has changed at all of GCC 4.9 stable vs. GCC 4.10 (GCC 5.0) I compared the performance of GCC 4.9.1 against the GCC 4.10 20140810 bi-weekly development snapshot. Both compilers were built the same from the Ubuntu 14.04 x86_64 Linux host with A10-7800 Kaveri APU. The CFLAGS/CXXFLAGS compiler flags were maintained the same for both compilers.
Overall there isn't too much to get excited about with these GCC 4.9 vs. 4.10 compiler benchmarks on the A10-7800 "Kaveri" setup but you can find all the data via this OpenBenchmarking.org result file. For the most part the performance is the same but there's a few areas of differences.
More Intel/AMD x86 and ARM benchmarks of GCC 4.10/5.0 will come when the state of the code-base is more distinctive from GCC 4.9 stable.