@freevito,
You may want to ask Yazsoft directly about the upgrade path. As you mentioned, their support is quite good.

I've used Speed Download since the first version came out, before it became a Yazsoft product. Overall I've been very happy with it, and was happy with my upgrades up to version 4.
I avoided version 5 until I bought it as part of the givegoodfood2yourmac promo. I only bought it since discounts were higher the more programs a person purchased as part of that promo, so buying Speed Download enabled me get a better discount for the applications I wanted, and the price was the same or lower than buying an upgrade.

Regarding version 5 the old Floater is gone, and instead users can minimize the main interface. According to Yazsoft this was "a serious upgrade." I wish they would include the option for users to decide whether to use the old floater or the new minimized Speed Download. The floater had the advantages of being smaller, displaying the number of downloads, and being independent from the main window which was important for people who liked to use both elements of the interface.

Gone are other features as well. For example, the toolbar used to have icons to Hold or Queue the downloads. These commands are no longer available via the toolbar, although they're still present via a contextual menu. In practical terms, it means wasting more time to invoke those commands. Instead of using one click to achieve a goal, users now have to click twice. First to access the contextual menu (and wait for the menu to appear), and then to select an action.

Version 5.1 crashed constantly. Yesterday 5.1.1 became available and the release notes indicate that it is "Optimized for Mac OS X 10.5.6" so hopefully that will eliminate the crashes.

Up to version 4 I would rate the program with 5 stars. I may actually go back to using it instead of version 5, which deserves only 3 stars.