My DS8 is in 8th grade and my DS6 is in 4/5th grade. When it comes to "pushing", I have found that some pushing is needed so that boredom does not creep in and then the emotional and social issues start croppoing up [ An idle mind is the plaything for the devil ... so to speak )
i had both boys accelerated to the point when both of my boys say schoolwork is no longer boring, then I feel I have got them at a level that is challenging but not overly so.
Also intorducve them to non-academic but mental stimulating challenges like the language yiu are doing and maybe music as well.
Also try to aquire acedemic material that may be just a bit ahead of where they are and leave it in their room to discover and work with on their own timetable. Encourage and praise them when they are doing that sort of work but do not set goals, let them "freeform" on their own.
