"though overall" is correct and is commonly used in written English.
Example: Though overall the test results were positive, there were still areas that could be improved.
I definitely think they helped, though, overall in averting a much more serious recession.
Steady progress on investment continues though overall returns have slipped.
Correlations between groups were an order of magnitude lower, though overall significantly positive.
Even though overall network audiences have eroded significantly, the evening newscasts have remained relatively stable.
Fire frequency was similar to early Holocene though overall charcoal accumulations were reduced.
This has all occurred even though overall television viewing levels have remained relatively constant.
Though overall unemployment is at a record low, manufacturers are laying off workers.
Though overall credit growth had increased it remained below that of nominal GDP and below pre-crisis averages.
Consequently, Birmingham club crowds tend to be dedicated and discerning, though, overall, the scene is relatively small.
Without compensation the project would imply a net loss for Poland, though overall there is a clear net benefit.
The report found that even though overall holiday sales were sluggish in 2007, online sales remained strong.
