Depending on what your stock rev limiter is set in your computer the msd box wont do any good for aything around 5500rpm. Your stock rev limiter will kick in first untill you get it changed.
I have the 6K pill too. With the stock shortblock, the 5.0 makes most of its power around the 5K mark so you really don't need to be pushing it more than 5800 really. Anything beyond that is just winding out the motor more.
I too have the 6000 pill. But if it's stock, it will die off before that. But now with the rebuild and better equipment I plan to install the 6500 rpm pill. Oh by the way I recently purchase the Tweecer and will be disabling the factory rev limit to test the claims of the heads, cam and intake of being good upto 6500 rpm. Just One Man's Opinion. Peace.
First the twEECer users here have already provided data that our stock rev limiters are set from factory *ready for this* 7000 so it's not going to stop at 6250 unless you have the fox puter. Methodical you will see when you get your twEECer where the limiter for yourself.