Actually...
the warhead on the Neutron-S missiles is longer than the Ikazuchi and larger in diameter than that of the SDF-4 Izumo!
This was submitted to Rtsurfer's website by me from my copy of Artmic Entertainment Bible #16 (rts sadly forgot it was me and listed it as being submitted by Zor_Master). Since ImageStation is stingy, I recopied it (had gotten deleted from my HD) and reposted it at ImageShack.
http://img15.exs.cx/my.php?loc=img15&image=ArtmicEntertainmentBible01.jpg
Quite simply, the Neutron-S missiles are fragging HUGE. Given that, its probable that the original missiles (not the ones we see in TNG, they're probably 2nd Generation ones) were the 'cruisers powerful enough to destroy the Earth in one blast' that Exedore refers to as being built in the Factory Satellite during eps. #30
Viva Miriya. Its likely that the original missiles were used during the long campaign the Pioneer Mission undertook to find the Masters' homeworld.