Those formulas are all well and good (though I personally do the speed correction (- 30% for Tourney greens) on the basic displayed length, then adjust for elevation change, and finally add a 'safety factor' of 1.5 ft.
Why? Because (assuming WGT has the physics right!) green speed is a friction factor and only operates over the actual distance rolled; elevation changes, on the other hand equate to the 'gravity help' you get to subtract (for downhill putts) or the'gravity penalty' you need to add (for uphill putts)to raise that ball up x inches.
BUT! Those calculations assume a constant slope up or down to the hole. However, all bets are off if you're putting from a lower tier to an upper tier, or vice-versa.
For these cases, it's best to break the putt into 2 parts:
1. if going to an upper tier, figure what it'll take to get the ball up the hill to where it levels off; if going to a lower tier, what will it need to get the ball to the 'cliff-edge' of the down-slope? If the ball is going to break hard moving from one tier to the other, drag your aim point to the upper edge of the 'cliff' and a spot that you hope will allow your ball to end up close to the hole at the end of its roll.
2. Now figure the last part of getting the ball the rest of the way to the hole, and add the two results.
Note - if using the method above, only apply the 'safety factor' I referred to at the beginning once - to the step 1 calculation. Otherwise you'll blow by the hole.