Can you post your comparisons ? It might start shitstorm but it's always fun :- )
I could believe you're able to get faster results with Octane if you have (few) fast GPUs, but iRay ? The slowest engine of the planet ?
When I and friend (Lasse Rode) did comparisons, iRay came extremely slow. To me it was far slower than Maxwell in CPU mode. GPU mode could not salvage it.
The only studio I know who use it in production (Delta tracing) claim rendering time for hi-res finals to be few hours using 6+(!!) Teslas20xx, so like 580GTX in performance regard or something close to that. That's not what I would call fast...
But I like the results.
What's different "pt" method ? What and why are you changing ?
Tricks...there are no tricks, that's the benefit of Corona, there are no secret settings you need to discover. Just abide to proper rules that are renderer-agnostic.