Here are the optimum shift points for the Stock Audi A4 1.8tqm.  The hp/torque data was taken from the Wetterauer web page and 205/55R16 tires were assumed.  The green lines are the rear-wheel power curves (in kWatts/10) for each forward gear, assuming no drivetrain losses, since the Wetterauer data was wheel data.  The yellow lines correspond to engine RPM.  Please keep in mind that a different final drive ratio or tire size will shift the curves in the horizontal axis (shift point speed will be different), but the optimum shift point RPM will remain the same.

Audi definitely did a good job of choosing the gears for the low pressure turbo 150hp engine (assuming you have your rev limiter at 7,100 rpm).  1st and 2nd are spaced just right to get the best 0-60 times and the engine would be turning right on the power band in top gear during actual top speed of about 130mph.  Still, 5th gear is quite close to 4th and a taller 5th (like from the 30v A4's) gear could be used for better fuel economy without hurting performance.  Unlike chipped, high-pressure, engines, the final drive ratio of the A41.8tqm is well suited to the power and torque characteristics of the stock engine.  In fact, putting a taller final drive ratio will make the car feel sluggish off the line, will give slightly better gas mileage, but will have a detrimental effect on 0-60 times.