I've done it constantly and have otherwise driven it hard for the past 50k miles that I've had it and have had absolutely zero problems a as result. It still runs like new. I even accidently misshifted and hit 8k once.

It is true that your power really drops off after 6k on a LS, but it's still beneficial to shift in the red because staying in the lower gear delivers more torque to the wheels. I'm not sure what the optimal shift point is for a stock LS, but based on the dyno of my LS with I/H/E, shifting at approximately 7100 rpm will deliver the most torque to the wheels. That's based on my engine's torque output up to 7200 rpm, gear / final drive ratios, and the calculated actual torque at the wheels (the dyno plot factors out the effect of gearing, but I put it back in).