If you have more money I would probably invest in bit coins if you think the currency has a future, but not in a mining rig.
Depends. A 6950 is still a viable gaming solution, doubly so if you luck out and get shaders unlocked. It, as a tangible good has a value (well over 50% of the purchase price ATM) to a vastly larger market than bitcoin enthusiasts.
7 series cards are not going to show up until late fall, so that won't change for ~3 months. Let's conservatively say the depreciation of a 6950 is $120 over 3 months, for a final ownership cost of $120. It is possible to recycle a an obsolete PC for the rest of the rig which won't depreciate nearly as much.
Anyway, that is about 8 bitcoins worth of depreciation worst case. The same 6950 may not return 8 bit coins over the next 3 months adjusted for difficulty jumps and power costs. I think 6 is a likely estimate (most of that being in the first 6 weeks).
Bitcoins have only the value buyers assign to them. They could be worth $100/btc by fall, or they could be worth $0. In other words, investing $ in bitcoin is far riskier, but has a chance for a larger payout over 3 months.