To increase the speed of Shareaza you MUST decrease the number of upload slots you have in each queue.
By default, Shareaza sets 5 upload slots for each of the 5 upload queues it has which fragments your upload bandwidth by 25 (this is not good)

Go to - Tools - Shareaza Settings - Uploads, Then click on a queue and press 'edit'. There, on the top-right of the window, 
In the 'Capacity' section,  set the 'minimum' and 'maximum number of transfers' to 1 or 2 not more !! (lesser is better)

Finally set the 'maximum number waiting in queue' to 20 and make sure 'Bandwidth' is at MAX or at least 100 Kb/sec

If everyone does this, the network and download speeds will increase substantially.

Cheers !