I disagree. I too am a strat owner but not a trem user, and I found that using the full 5 springs added a touch of sustain (when combined with screwing the claw right in). As a result the trem is un-usable, but that's fine with me. More springs will make the guitar feel slightly tighter, more like a hardtail but remaining the strat-with-trem sound, and it will bring the trem block into the body with more tension. This, to me, is what gives the extra ounce of sustain.
There's other important benefits too. Firstly, your tuning is much more likely to remain intact if you break a string with 5 springs. Also, you'll practically eliminate any trem sag (try hitting the low E, then bending up the high E from G to A.....you'll see what I mean).
At the end of the day it's a very cheap and easy mod to make, and to reverse. Best of luck with it.
Jordan.