Buying latex tubes for performance? Save your cash. I am highly skeptical of any measurable power savings, but even so, you are going to kick yourself when you go through 3-4 at a time as is known to happen.
Stick with standard Continental or Michelin tubes. Tube weight won't make a lick of difference at our level, so go for cheap (relatively) and reliable (think valves). I bought 20 or 25 conti tubes from PBK about 6 months back when they were ~$3.50 a pop. They're great tubes for the money, so I'll pick up another batch if a similar opportunity presents itself.