This is something that no one can answer *for* you, but they can certainly assist you in seeing the differences you should consider when making your powerplant selection.
Recommending the level of power to someone is like recommending the type of girl you should marry. Only you can or should make that decision, because you are the only one that has to live with it. ;-)
What are *you* comfortable with? TRY it first and let your first impression be the judge. If you're not used to big power in a small car, be careuful.. If you *are* used to it, then still be careful!
Choosing a big block or small block is like shooting guns. You might have a .44 magnum and not hit a thing, but be deadly accurate with a .38. Then which would be better... for you? This might be more the reason the small blocks are said to be better on the track than their slightly larger bretheren. Less fear of the car itself, not the actual handling differences some might think. This is especially true in the very rigid and well handling SPF, which doesn't seem to differ much from small to big block any way.
However, with the big .44 magnum and you may never have to use it, which is why at car shows and on the street the Big block usually are respected as the most intimidating thing out there, and may very well keep you from HAVING to prove it, just by having it under your hood.
You can make nearly as much if not MORE horsepower with a well built small block, however, usually you can make that same power more relaibly and cheaper with a Big Block (429/460 series) because the inherent strength is already there in metallic size, not structual expense. On another note, the FE (427/428 series) Big Blocks will cost significantly more for the same results, and do not skip in this area with this series engine, ever.
But of course, if you are really not going to use all that extra power, then it can be more of a nuisance than a benefit... kind of like having a dually long box four door crew cab pickup and only tow a trailer once a year. For some it would still be worth having it. However, for many, it wouldn't... again, the personal preference is the final factor in any decision such as this.
I have both a small block Superformance car _and_ a big block Superformance car. They almost weigh the same (125 pounds difference), feel the same (in ride and street handling) and handle darn nearly identical in the turns (not hardcore racing, but spirited street and country road corneering, etc). However, that's where the similarities end.
The big block's sound is deeper, however not different enough to tell people it's different other than trained fellow cobra owners. The G-forces the big block puts out is, well, darn right scary and certainly dangerous in the wrong hands... even the right hands on occasion. The small block is a little more forgiving with throttle "mistakes", and may have an edge in short course autocrossing events where every single pound counts when racing against Miata's and the like.
The Big block I have (750hp) gets 17mpg at best, and averages 12-15. The small block I have (450hp) gets 23mpg at best and averages 13-18.
All engines will respond differently depending on their build and how racidal their cam/porting is, so these numbers can vary greatly, but usually in proportion to each other.
Niether is better or worse, but again, it's really abut what *you* want, what *you* expect and what *you* are comfortable with, and certainly, what *you* can handle. Now is not the time to use the machoness we guys all are born with... because saying, "ah, I can handle it" may be the last words you speak.
and remember when making your decision, that you may not be the only one driving your car... if your wife is not comfortable with driving it, that may take a lot of the fun out of a previously thought of "joint pruchase" into what "you bought yourself"... and you know where that can lead! Remember, you need an excuse to buy more stuff for "our" Cobra in the future, not "more crap for YOUR car"... lol... these words have been repeated by many a spouse in the past... heed these experiences.
The best advice anyone could ever give you is go to your local Superformance dealer and let them take YOU for a spin in Superformance's with several powerplant types such as a Mild SB, Radical SB, Mild BB and a Radical BB. If the dealer does not have all those variations you seek availble for driving at the time, they will certainly assist you in finding owners in your area to give you a test drive in the various options.
You shouldn't base your final decision on price, durability or fuel mileage of any of the choices, since they can be made very similar in the end result. Use them as factors, but not as the deciding one.
Unless you are hard core racing, I wouldn't use a few pounds either way as your desicive factor. First, lean towards what you "want", or have wanted all along. Then go out and prove to yourself if that's will be the right choice in the end. Sometimes just the underhood appearance is the factor all in itself. Sometimes it's the "drivability" of being able to hop in your car and take a 15,000 mile trek across the country like this guy did...
http://performanceunlimited.com/supe...e/usatour.html
Just be sure the "negatives" of your choice one way or another do not outweigh the positives. After that, there is no question that you have just made the right decision.
Please note I did not suggest which engine you should seek one way or another, because *you* should be the one making those decisions. Besides, I myself couldn't decide as well... so I got one of each! (although, I do have my favorite, but you shouldn't be making your choice on what my personal preference is!)
Hope this helps...
/Randall