Keep in mind you want to have some form of margin, so that way you aren't drawing max power through the transistor and therefore heating it up dangerously. Usually the rule of thumb is at least 50% and often 100% for certain applications. So if you want a single transistor that will conduct 0.84A through a fairly stable load (Which LEDs are), you'll probably want one that will handle at least 1.26A. Additionally, you can put transistors in parallel and have them control/sink different groups of LEDs, and also distribute the power then. Then you can either connect them all to a pin (assuming you don't over-load the 20mA limit per pin), or you can connect them to different pins and therefore can control them separately.
Also, keep in mind that absolute max values are hard limits and exceeding them, even briefly, will most likely result in damage to your circuit.
Another IC to look at would be the ULN2003A, which is basically an array of transistors. Its simple to use and is great for sinking LEDs and other large current devices.