It depends on your driving style and what you're trying to do...
...but if you were at the racetrack with your foot to the floor, you'd want the trans to upshift at the top of your powerband. The powerband is the RPM range where the engine really PULLS... you'll need a tach to find that out. For instance, when I hit 3000 RPM on my 2.8, the motor really seems to wake up- but past 5000 RPM, I really don't feel the engine pull any harder.
So if I was racing, I might put a linelock on so I could stage at as high an RPM as I could do without my tires breaking free (or suspension tearing out)... hopefully it'd be close to 3000 RPM, then when the light drops, I'm already starting at my powerband. Then its Zip Zip Zip thru the gears without any "dead spots".
A cheap tach is about $30-$40 and easy to install (hardest parts are finding a nice spot in the car to put it and then drilling a hole thru the firewall for the wires) if your car doesn't have one... see summitracing.com for a few. Local stores might want a lot more cash for one, but you won't have to pay shipping.
So if you're looking for your powerband, you'll need to read the tach.... | 
