Unfortunately I have yet to get my hands on any Loongson hardware, but on OpenBenchmarking.org it was discovered that Linux benchmark results are beginning to appear for the ICT Loongson-3A V0.5 FPU.
The Loongson CPU information confirms the quad-core MIPS hardware:
processor : 3The quad-core Loongson 3 variant at sub-1GHz speeds is said to consume 15 Watts or less while offering fairly compelling performance. Though most of the Loongson 3A benchmarks on the Phoronix-owned OpenBenchmarking.org right now appear to be disk/memory tests. OpenBenchmarking.org data is obtained via the Phoronix Test Suite software.
model name : ICT Loongson-3A V0.5 FPU V0.1
board name : Loongson-3A780E-1-V1.03-demo PMON_Version_V3.0R014B0044D0220
BogoMIPS : 718.84
wait instruction : no
microsecond timers : yes
tlb_entries : 64
extra interrupt vector : no
hardware watchpoint : yes, count: 0, address/irw mask: 
ASEs implemented :
shadow register sets : 1
core : 3
VCED exceptions : not available
VCEI exceptions : not available
The Linux software running on the Chinese hardware was Debian 6.0.3 using the MIPS64 version of the Linux 2.6.36 kernel.
Hopefully more MIPS64 Loongson hardware will begin to appear soon in western countries so that more extensive benchmarking can take place. Until then, see the Loongson data on OpenBenchmarking.org.