If your character really has a speed, I feel it would be better to do a count-up to a certain point / then you get to go kind-of-thing. Although you could (as Tharasix suggested) just double everyone's speed if someone gets to fractions, with a count-up (A la Final Fantasy type games), higher speed is better, so there's never any need for fractions, and your speed is always your speed, if you catch me. Basically, envision a speed of 1 as the slowest possible speed for someone to act in battle: perhaps an automated mortar or something that fires once every few minutes might go into fractions or decimals, but that would be the exception. Then, give each action a duration, like, firing a grenade launcher from the hip, and if that action takes longer than your speed score you adjust it. Otherwise, you still take your speed in segments as a sort of reaction time.
Now, I find the alternative much more exciting. Keep the build up method, as Charon originally stated, but don't have a generic 'speed' for your character, because that is not really something I can contrast in life. An expert fencer who's never fired a gun will not be able to effectively operate a revolver as fast as he can slash and thrust. Instead, let the person's skill with the weapon (or skill... fast computer hacking/spell casting/bomb disarming anyone?) lower the action time from the standard value. Come up with an initiative that helps a character get started, if a character has a speed stat it could be subtracted from a base value to figure it out. each technigue you have takes an amount of time (you could call this speed, but it's more appropriately slowness).