Go 1.8 has a few new 64-bit x86 instructions supported, Go 1.8 now uses its new compiler back-end on all architectures (with Go 1.7 their new compiler back-end was just used on 64-bit x86) and that should yield a 20~30% performance improvement for 32-bit ARM systems. But even x86 64-bit systems should see 0~10% performance improvements with Go 1.8.
Also improving performance with Go 1.8 are garbage collector improvements, overhead of deferred function calls was reduced by about half, and the overhead of calls from Go into C with Cgo was also dropped by about half.
Go 1.8 also has a variety of run-time and library improvements too.
More details on all of the changes for Go 1.8 via the project's release notes.