Besides endorsing what the others have said, I'd add a couple of subtleties to it.

Use the 2 RUs for the outbound flight, because if they don't clear because loadings are full, you can always use them for the inbound. Otherwise, use either Expertflyer or do a dummy booking and find out how busy BP is on each flight, and pick the less busy one to increase the odds of the RUs clearing.

Of course, if you get it on the outbound, you'll find the inbound painfully disappointing by contrast, but still I completely agree with the others. Using the RUs on the 777-200 PE is a waste. A bit of legroom, recline and better meal on two flights is nothing compared to BP on one. Besides, you can always do a not too pricey OneUp for the other flight to PE.