I always fly with my wife (who is also a 1k) and we have a 100% success rate applying our GPUs over the past few years. We only use them to secure lie-flat seats on TPAC and TATL flights.

I have found the spread between the lowest and W fare to be between $100 and $800 with the TPAC spread larger than the TATL spread.

I have always waited until I was able to find R > 2 space before booking. Now I usually need to search multiple routings and be flexible with scheduling in order to find free R inventory. For example if we're flying to Asia, I check EWR/ORD/DEN/SFO/IAH (etc.) - NRT/ICN/HKG (etc.) looking for R space. If we're flying to Europe, I'm checking EWR/IAD/ORD - LHR/FRA/BRU/MUC etc.

But so far at least, it has worked for us.