I use raw at times on my Oly E500 when I am doing prime focus thorugh my TV85 scope,, raw shots are a tad over 10mp on my camera, TIFF is up around the 13mp area,, certainly larger than the 5-6mp at the best jpeg level,, you will also need to assure you have software that will handle the raw image from the camera,, most software does not handle,, you can download rawshooter essentials from the web for free,, really has some nice features to it,,
write time for true raw is going to consume more file space in the camera, slow the cameras operation down (depending on your cameras speed to store before writing) and to download to your computer will also take more time,,
not many cameras will allow your rapid shooting while in the raw mode,, those that do are in the high $$$$ range,,