Welcome to the forum. I'm sure you will find some very helpful info from Saleen owners here.
One thing to consider, it is generally accepted that 450 hp to the wheels (about 530hp with a manual trans) is the max the 4.6 engine will handle without forged internals. So if you want 550 hp or more, you should go with the E or be prepared to spend some $$$ upgrading the SC's engine.
I have an '06 S281 SC and considered the E. But I believe I have all the power I need for what I would consider safe street driving (of course, "safe" means different things to different folks). I drive my car 2-3 days a week, including occasional commutes to work, and the thought of driving a 550hp E in Los Angeles traffic (especially if the throttle response is as touchy as dotbomb mentioned) seems like it could be more of a chore than a joy.
Another potential Saleen owner (who ultimately bought an '06 SC, I believe) asked for pros and cons of Saleen ownership on another Saleen forum and this is what I posted:
Pros:
Power -- 435/475 hp is more than you'd ever need unless you're on the track
Handling -- remarkably improved over the base GT; MM&FF magazine had it beating a C6 Vette on the track
Design -- nothing short of striking
Saleen Ownership -- fellow owners are a helpful bunch
Sound -- I love the exhaust note
Warranty -- (note the '07 models have a longer warranty than the '06 models)
Exlcusivity -- very low production numbers. Here in L.A., I see AMGs, M series, and 911s on every corner and even Astons Martins, Maseratis, and Ferraris fairly regularly. I never, ever, ever see '05-'07 Saleens.
Muscle Car Feel -- When I first bought my '67 Pontiac, I remember thinking it was a shame that nobody builds cars that feel or sound like this anymore. The Saleen comes closer to combining that late '60s muscle car era feel with modern performance and technology than any other car on the market that I know of.
Cons:
Service -- Not many Saleen dealers out there. And warranty work can take a while (since they don't normally keep Saleen parts in stock)
Ford Dealers -- Although you're buying a $50k+ car, you're not getting top level service from Ford sales/service managers
Limited resale market -- since few people know what a Saleen is, it can take months to sell a used one
Ultimately, I love my Saleen and still look forward to every opportunity I get to drive it, even after 6 months of ownership. Simply put, I would not consider another vehicle out there for the price.
Not sure if that is the kind of info you are looking for, but if not, just ask and yee shall receive. Good luck with your search.