Well on the maths side - I'll compare them so it may make a little sense
A PPS pool (and when I say PPS I do ONLY mean a true PPS) pays you a fixed amount (don't forget to remove the fee).
So certainly with renting and pointing it at a PPS pool, you must be paying less for renting, than the PPS pool's stated payout.
Simple to compare the cost vs the payout and you clearly win or lose based on that.
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A PPLNS pool will have an average expected reward (here it's 98.7% PPS)
Pool luck history will show some other value (close to or distant from that)
I have related numbers on the Blocks page on the web site.
But PPLNS is based on block finding (i.e. it reflects what you are actually doing)
When the pool does something good for bitcoin, we all get a reward.
If the pool doesn't find a block, we don't get a reward.
Thus it is the luck of block finding that determines your reward.
You can't guess that in advance and be guaranteed to positively affect your reward, no matter what anyone tells you.
So the simple answer on any such pool (which also includes slush) - it's luck that decides if your rental will make more or less than PPS.
However, from a statistical point of view ...
The longer you rent, the lower your expected variance will be.
This means you should expected to push closer to the expected reward (but still would be expected to be above or below it)
The shorter you rent, the higher your expected variance will be.
This means you could vary much further from the expected reward (positive or negative)
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Aside: ignore CPPSRB - that's even worse than PPS
It has an upper limit below 100% PPS ... but that's the absolute limit ... what you get can be anywhere from that or lower (never above)
... and the only pool using it spends a LOT of time working on stale work and also gives you bad work (empty blocks) every block change even though >90% of those empty blocks are slower than good work here.