No, you should always buy the fastest single card you can afford. Only worry about SLI/CrossFire if you buy a larger monitor but don't want to trade out for a newer (and likely more expensive) video card. At that point, upgrading to dual cards to save some money is where it makes the most sense (unless you buy both high end cards at the same time)
I speak from experience on this part, but you can decide how you want to go either way.
The write speeds on that Crucial drive really
suck, if you're trying to keep yourself on the cheap side, it would be fine for light to medium use, but if you find that its performance is underwhelming, don't discount the importance of fast writes.
If you can wing it, this drive is bloody fast for the price: (capacity is just about the same too)
Newegg.com - Corsair Force Series GT CSSD-F60GBGT-BK 2.5" 60GB SATA III Internal Solid State Drive (SSD)