Nah man, everyone is giving you bad avice. Forget about your own saddle - hey its just a saddle, they're all the same right? so long as its small and triangular it works just fine, dont worry about it.
And for the sort of distance you're doing you have to get as low and aero a position as possible. The greater the seat-to-bar drop the more aero you'll be so you'll have less wind resistance and finish every day feeling much better. The skinniest tires pumped up to the highest possible pressures will help in this regard also.
If you get a new bike get the lightest and stiffest frame you can find because its more efficient, the less wheel spokes the better.... and don't adjust anything at all - it was designed and built by specialist engineers that know more than you so it must be right.
Forget about taking any tools or spares and never fill your one waterbottle more than 50% because you want to avoid carrying weight. Just look at the pro racers, they don't carry tools, and they're professionals!
Now go do the opposite of all the above.