Personally, I’d inspect the cards first and judge if that’s a condition you’re happy with. If so, I’d crack the slabs and submit the cards raw. I believe that’s what vast majority of people on the forum would recommend. At least anecdotally, the crossgrading service seems to be quite often unseccessful.
Also, this question would likely be better suited for this thread:
www.elitefourum.com/t/the-giant-professional-grading-thread/30930/1