If I recall correctly, 16S is 5.56 and 17S 7.62. The key question is, what is the future caliber being envisaged by the Pakistani planners.
Also, keep in mind that amongst the western suppliers, Belgians are considered fairly expensive. If Pakistan were to opt for a western system, we should simply go to the Americans and agree on something. Massive economies of scale and competition among American small-arms manufacturers may make sense.
Given the recent purchases by the UKSF of
Knight's Armament Company (KAC) KS-1, Sig's deal with the Indians on the basic 7.62 platform and a brand new platform for the USSOCOM are good exmples and I think Pakistan should explore this route if domestic efforts and collaboration with Turkish/Chinese sources aren't meeting GSR.