Go attack on Gelgoog Cannon. The missiles will be incredibly powerful.
Oh, and don't go spec on something that doesn't have funnel skill. Even with spec up you still won't be able to 0HKO S ranks without it.
If you're happy with attack then put some in speed. Goog C is a mid range unit. Sometimes you want to be fast.
SDGO? I liked it better when it was called Space Marine.