Will the card boot a RAID 0 Stripe of two SSDs on MacOS X?

Haven't done it myself. But pre-purchase research indicated: YES.

Do both SSD's run at maximum speed on this card?

6 Gbs is the SATA speed in this card. Both drives will run at native - theoretical speed, paper printed speed is one thing, your PC setup will determine the final speed, when the dual card is configured in RAID mode, there's a bump in read/write data, not perceptible as SSD are faster than a HDD