There's a lot out there about knobby tires not being able to go fast. I don'y not understand this. My tires are 26 x 1.95 and really knobby. I find I am cruising just fine... I don't even want to try slicks, they're that fast. I can't be the only one who has this opinion....am I?
The less rolling resistance, the faster the tire and less energy it takes to make it roll. Big knobs and soft compounds produce more resistance and will be slower and sap more of your energy than lower profile knobs and harder compounds. With tires there is always a trade off. You have to consider the type of terrain that you ride and what's more important to you, traction or speed. Tire size is also a factor. 1.95" tires are on the small side for a mtn bike but are going to be faster than the same tire in a 2.1" or 2.3" etc...
I would just go with larger knobs (in diameter / height) that way you have more diameter to the wheel and more resistance against the tire itself digging into the ground yet also the protection against flats and added traction.
I have Panaracer Fire XC Pros, Pump them up to 60lbs, They fly with enough traction for me. Feels like my old school bmx bike.