Best flags usually are:
-O2

With sometimes -Os being better, depending on your application. If it does lots of 32-bit floating point operations, mfpu=neon might also help. Benchmark as necessary

Half of the stuff you're specifying is already the default in scratchbox (mcpu, mtune, fomit-frame-pointer, mfpu=vfpv3, mfloat-abi, mlittle-endian),
the other half is contradictory (mfpu=neon when you also specified mfpu=vfp ?) ,
and some do not exist (O4, O5, O6, ...).

My suggestion is that you use as few flags as possible.