One thing to remember when "loosin'ing" up the machine is that the stats are based on 10million spins.
So a 98% chip could pay out the top award of 10000 coins and then not shed a quarter for the next 3 years and still make the 98%.
On the other hand you might see the machine paying off daily in small payouts (usually less than what you put in) but never hit a top prize for 8 years.
In a household setting your going to see much of a difference from a 85% chip to a 98% chip on a day to day basis.
Don't get me wrong - I am not saying to NOT put in the highest payback percentage you can find, just saying you might not notice the difference.