Thank you very much for good explain. Have you found the bugs in module that you have tested ;)
We talking about compatibles. You can check by yourself all change list from PS 1.7.8.0 and you will see above version haven't not core modification! This is rule same for modules and themes. And...
Hello. If thinking as you then 1.7.8.4 not last version too. Last PS 1.8.7.5. Since 1.7.8.0 in minor version (last digit) the developers only fix the bugs, without core modification.
For my opinion, and I'm sure the Leo 1782 will be work good on PS 1.7.8.5!