On one hand, your loans cost less than investing would return.
On the other hand, there's always a question of loan freedom vs most money earned. Which is more important to you?
If you choose investment - I'd probably split that up into 4 sections, equally priced. 25% each into big cap, small cap, emerging markets, and bonds/notes. As long as your strategy is reasonable, and you rebalance once or twice a year, you'll be fine.
One wrinkle I see is if your variable rate mortgage jumps. Will you be able to refinance?