The E-PL7 was (is!) one of the nicest PEN bodies Olympus ever made - it feels better in the hand than even the also very good E-P5. The E-PL8 is comparatively slippery and fiddly - worse than the somewhat barren, but pleasantly slick and small E-PM1. The innards of the E-PL8 are almost identical to the E-PL7's - there's only a couple of minor software "enhancements" I certainly wouldn't bother about. The sensor and I.B.I.S. are the same. The E-PL8 isn't worth it over any other PEN, older or newer, that's my personal opinion.
The E-P5 is an almost professional grade camera, very competent indeed (the only thing it truely lacks is weather sealing). In the hand, I prefer the E-PL7, though - so if you need a fast camera with very good IQ for casual shooting, I'd choose the E-PL7 even over the E-P5. That said, if the price for the E-P5 is right, this is one serious powerhouse that's still pleasantly small and handles great. So if there's an E-P5 available for a reasonable price (sorry, I have no idea of what that would be in Australian dollars), I'd go for that, no doubt whatsoever. If, however, there were also an E-PL7 to be had at the same or a little lower price, that's what I'd get. The E-PL8 gets a no-no from me - I held the camera at Photokina and felt almost cheated, knowing that it was an E-PL7 in cheesy disguise.
To use an analogy: The E-P5 is a slick sportscar with a seriously powerful engine - little compromises made towards casual use, but still capable of being used as an everyday car, though less suited for travel for those who like a little comfort. The E-PL7 is the funcar version - less power, less roar, but a little softer in the suspension, top raised to allow for a little more space for everyday duty while not giving up much on the road. The E-PL8 is the bling variant - the cabriolet version, quite nice to look at, but something you wouldn't want to have to drive in cold and wet weather; still fun, but only if conditions are right. Which one would you choose?
I just rediscovered the E-PL7 - it's a fast camera that's ideal with the small primes available for
(it can handle the bigger lenses - but I prefer the small packages much better). I'll take it for a casual roll next month with three primes just to celebrate the strengths of this underrated little camera. I had the intention of replacing it with the GX80 - but it stuck around for some reason, and now I'm glad I hesitated ...
M.