Optimizing an IP generation method
I have performed some benchmarks to get the optimum combination of block and slice sizes using 32-bit and 64-bit compiler. 64-bit because we are also developing an optimized 64-bit implementation on the sidelines. Here are the results for generating 320000 IPs on our server with all the server applications also running, the values are in Milli-seconds and floored over 5 runs;

Block-Slice  32-bit 64-bit
32-0         3479   3120
32-16        3464   5912
64-0         2059   2980
64-16        2028   1606
64-32        2013   1622


The algorithm gave the worst results with 8-bit slices.
So the best bets are 64-32 for 32-bit and 64-16 for 64-bit for this algorithm.