also, do a search for e107 mods for SEO, see what other people have done to modify their default installation the only caveat is if you change the mod_rewrite rules and your pages already have PR, they will lose them
I think you have answered your own question there. Thats like saying "If I optomize my body by going to the gym, will I be fitter?" Using a CMS has nothing to do with your Search Engine Rankings. As long as you have good optomized content, you have just as much chance as ranking high as someone with good optoimized content with static content.
My main keywords are Naruto, Anime, and Manga. Most of my top competiters volume 30-90k unique visits a day and all pay to have SEO done to their site so the competition is really tight.. espeially with SEO optmization. Most of my visits come from specific attractions on my site and not much from search engines.
That's not even close to true. If the CMS hasn't been designed with SEO in mind, there's a good chance the default config could hamper your rankings