Fast is not light until you are at that elite level .........
I used to race my 21 pound Colnago with Chorus stuff just for a change from my 19 pound GT with Dura Ace and all super light components.
I even broke out the 23 pound Fuji Team that I used for rainy days with down tube shifters and a Spin rear wheel and did well. And sometimes I'd even place better with the bike ......
Fast is miles and miles of training, good diet, and persistence. Fast is not a light/latest technology bike.
But for arguments sake, I'll give you some answers ........
You need to ask yourself what type of material you want in your frame. Your choices are steel, aluminum, carbon, and ti. Each has it's plusses and minusses. I'll try to give you a few here for each:
Plusses:
Steel - responsive, lively, stiff but not unyielding, fairly bulletproof, very adaptable to any sizing
Ti - light (if not designed to be stiff), fairly responsive, corrosion resistent, light
Aluminum - very light, very stiff, corrosion resistent
Carbon - excessively light, can be stiff if layered right, corrosion resistent
Minusses:
Steel - tends to be more on the heavy side (not always the case), will/can rust
Ti - tends to be very flexy, can be brittle if not made by a top manufacturer, expensive
Aluminum - tends to be WAY too stiff on longer rides, breaks and dings easy
Carbon - expensive to get a really well designed one, tend to be very flexy if not designed right (lighter tends to be more flexy), warranty length of time issues
The frame will make or break a nice bike .......... it is the heart of the bike. Components will make it nicer, but if the frame does not suit you, you will hate the bike even if it is topped with the best components.