I do plan to get [an NV silencer for 5700] to test against my 5800 Ultra collection.
The Arctic NV Silencer2 is not an exact match for the 5800/5800Ultra, but it is acceptable. The NVSilencer2 screw holes are in the proper positions to actually mount on a NV30 reference PC board (unlike the NVSilencer4 that AC says fits the 5800).
The problem with the NVSilencer 2 is that the copper RAMsink pads leave two of the eight BGAs 50% uncovered. I suspect this is not a critical failure, but heat will decrease the lifespan of hot-running DDRII RAMs compared to full coverage.