Tip No 1
Get a bigger internet pipe.

Tip No 2
See Tip No 1

Multiple clients sharing a Fat pipe is acceptable / desireable.
Infact it is impossible to coax much more than 2 million URL's a day out of the client regardless of the bandwidth available

So the only way to up production is to increase the number of clients.

I have found that 1 client with 200 crawlers will keep an 8Mb ADSL
connection pretty much maxed out and 2 clients will make an ADSL 2
connection beg for mercy.