I own a Cannondale Quick 4.
I love the bike and have no complaints.
...and I have some in-store credit at my lbs.

If my desire is to make my Quick faster...
Would you upgrade the tires and wheels?
or
Would you upgrade the drivetrain?
I have about $250 in store credit and am willing to add another $50.

Specs:
Frame - Quick, butted 6061 alloy, SAVE
Fork - Quick Carbon Blades, 1 1/8 steerer
Crank - Shimano M151, 48/38/28
Chain - KMC Z72
Rims - Element Xero C3 Wheelset
Spokes - DT Aluminum Nipples
Tires - Kenda Kwick Trax 700X38c
Pedals - Quick Reinforced Compostie w/ Kraton, by Wellgo
Bottom Bracket - Tange Cartridge
Rear Cogs - Sunrace CSM668, 11-32, 8 Speed
F Derailleur - Shimano M191
R Derailleur - Shimano Alivio
Shifters - Shimano Alivio
Handlebars - Cannondale C4, 6061 Alloy, 25mm rise
Stem - Cannondale C4, 6061 Alloy
Headset - Tange Custom Si
Brakes - Tektro TX 120 V Brakes
Seat Post - Cannondale C4 6061Alloy,27.2mm
Wheel Rims - Element Xero C3 Wheelset
Nipples - DT Spokes
Saddle - Cannondale Quick Ergo Performance