Hi Gil,
If the biggest concern is data entry speed (ie entering one distribution code instead of 2), then certainly using the Tax Included type for distributions will help. If you use this, remember that you enter the amount with the GST included; the process automatically separates the tax from the sale.
Distribution Sets are basically just a collection of distribution codes or GL accounts that would be added as details to an invoice. If you find that you need to enter the same 5 distributions for weekly or monthly invoices, then this is a real time saver. When you create a new invoice in AP, at the right side of the screen is a button labeled 'Dist Set'. Select the required Dist Set code, and each of the defined distribution codes or GL accounts appear one at a time. Simply enter the amount and hit the Enter key for the next detail.
If you wanted to look at how this might be set up, the Adagio Payables sample data has a Distribution Set code with particular GL accounts.
Potentially, you could create a Distribution Set that has a single Distribution and a second code for the GST account. Whether this makes entry faster than Tax-included distributions will be up to your preference.
Whatever you do, go to the File menu and select Options. Choose the setting to 'Auto add items on documents' to speed entry up considerably. After saving a detail on an invoice, the New Detail screen re-appears, saving you a few keystrokes.