There is another reason to stick with rotary carbs in gas trucks. When you have a slide carb, the throttle linkage must run somewhat lengthwise with the chassis. Because of this, when you run across a very bumpy section that causes some chassis flex, it will also affect throttle position. This causes surging though bumpy sections. Rotary carb linkages run across the chassis, and aren't affected by chassis flex.
To add to what others said above, the OS engines are great. If you race at tracks with good traction, and/or have a smooth trigger finger, choose the CV-R. If you race on dusty, loose tracks and tend to yank the trigger, you'll be faster with the CV. The only downside to the CV, is the poor fuel economy. 5 minutes to a legal sized tank is about all I could ever manage.