What sort of performance benefit can I expect by tweaking ?
Keep in mind that you can only optimize your end of a Broadband Internet connection, and your throughput is also affected by the feed your ISP is providing, the congestion of their backbones, the state of the Internet at the moment, etc.
With all this in mind, there is a lot of room for improvement on your end as well, and that's what tweaking does. Under Windows 9x/Me/2k, a 30% to 100% performance improvement is typical, and we've seen some connection improve by over 200% using our simple Registry tweaks and patches. Very few computers are tuned for high-speed / high-delay transfers out of the box, and by simply optimizing certain Registry entries you can increase your throughput noticeably, especially on high latency transfers, and if you're not at the limit of the line provided by your ISP.
As always, your mileage may vary, just try and find out for yourself. You can try our pre-made patches, or if you prefer to edit the Registry yourself, read the Tweaking section of the site.