How does stuff like that get done, should I be prompting someone or going at it myself?

I'd start by sending the author an email pointing to this thread at perlmonks and go from there.

With regard to blocksize. I just did some not-very-representative testing using the loopback address on my machine and with 4k blocks the maximum throughput I can get is 140MB/s:

C:\test>sock-rated.pl -O=4 -I=4 1000
svr: request for 1048576000 
1048576000 took 6.999 seconds. [142.89 MB/s]
[download]

By using 100k blocks, I can get that up to over 300MB/s:

C:\test>sock-rated.pl -O=100 -I=100 10000
svr: request for 10485760000 
10485760000 took 33.032 seconds. [302.74 MB/s]
[download]

Not a real-world test, but still 4k seems like a pifflingly small amount.