I don't know if 4 1/2" would require a new front shaft or not. It would be getting close to it's limits with the suspension fully extended. another issue comes up with a double cardon shaft up front. If you adjust the arms for 5 degree or higher of castor, the pinion angle will be off enough to vibrate. Vibration feeding into the 241 tc is a bad thing. They have been known to explode from that. On the other hand, if you adjust for pinion angle, you might be near 3 degrees of castor and have a flighty ride. A few JKs, mine included, handles fine w/3 degrees, but many do not. When lifting to the point that you need a double cardon ds, you end up compromising between pinion angle and castor. That's the reason I went with a 3" lift. I will run the stock shafts until the give up and then replace them with another pair of stock shafts that you can pick up for $150.
Just my 2 cents worth.
2005 LJ, 112" wb, RJ60's, ARB lockers, Fox Coil overs, 40" Creepies