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.
This is exactly my experience, and my method for using GPUs. All my business travel is domestic however, so my personal international travel affords me more flexibility in booking with GPUs. I'd probably be very frustrated if trying to use them for business travel when schedule trumps everything.