Sold a toy I wasn’t playing with… what to do with the money

One of my hobbies involves working on my classic car – basically swapping corvette suspension under it. during the initial phases of this project I bought a CNC milling machine to make a bunch of parts for it. But, for the last year, I’ve had other priorities and haven’t worked on the car much, nor will I need the CNC machine alot from here on out… So, I sold it. Long story short I got $4500 for it. I’m trying to determine the most mustachian thing to do with the spoils…
Current debt is as follows:
3950 @ 6.9% student loans, 56/mo
4250 @ 7.4% student loans, 72/mo
4930 @ 3.4%, Motorcycle, 140/month
192,000 @ 4.5%, house, 30 year fixed. House value is ~220K
2200 @ 0% for another 16 months, I’m using this to build an addition on my house.
I have $4700 in a 1% APY savings account.

I currently put $620 a month into a stock purchase program that returns, at a minimum, 15%, and at best, 15%+ stock appreciation. I won’t have access to this until jan 1, 2014. The plan was to use that to pay off the student loans.  I am using the 0% card to build an addition on the house. (Doing 99% of the work myself.)  I would hang onto the $4700 in cash ’till the project was done, then pay it all off. I add $800 a month (rent income) plus ~1200 quarterly (bonus) to the wad of cash for the addition, so by october, I’ll have enough cash on hand to pay for all but a few thousand of the addition.

So, should I hang onto this cash as an emergency fund (1% APY return)
Kill the motorcycle loan (3.24% return, and frees up $140/month), roll than $140 a month into the other student loan…
Kill one of the student loans (7% return, but only frees up 72 a month) and put that extra money against the other student loan?  It doesn’t free up the cashflow as much, but does eliminate a higher interest loan. And in 7 months I’d get that money back anyway to finish paying it all off…

Or, should I use it to start a vangard index fund? Seems like the debt I have is the same as average returns on one of these, and is gauranteed… so this isn’t as attractive.

Should I pay off student loan?

I’m currently 22 and planning to graduate this December with a Bachelor’s in Comp Sci. I have no doubt in being able to find a job that lines up for post graduation, and the further along I have gone in my degree I have gained scholarships to more than pay for my current tuition.

I still have loans though from Freshman and sophomore year. I have already paid off about $6,000 for all the unsubsidized loans I had.
So the only loan I currently have is a subsidized loan with Sallie Mae for $11,750 with rates between 3.5% – 5.3%.

I have saved up so far about $6,000 and it is earmarked to be used to pay off the loan for after I graduate. I hope to have enough by the time I graduate that I have no debt upon graduation. Tuition for this Fall is covered and I may even get a bit of my living expenses covered as well.

My question is: What should I do with the money in the mean time? Currently I’m keeping it in case of a rainy day or moving expenses for my future job wherever that might be, and since the loan is subsidized, I’m not losing anything by keeping it in the bank instead of paying it off.

At the same time I’m a little cautious about trying to invest it at a time that I don’t have any regular investing scheme and would only be a short term investment.