Marc, are you looking for something stronger than all axles on the Gen4 viper or just stronger than the 08 Gen4 hollow shafts? If the latter, than the dodge solid shafts are an option that come on 09 later Gen4s, I know guys on here who have snapped the hollows on 08s have installed solids. This is one selling point on getting an 09 vs an 08, although the HP potential on Gen4s being somewhat currently limited to about 600rwhp, there's not as much action on these as with earlier Gens, IMO. I know there are load specs on the forum somewhere for the two. But if you're looking at more than that, I'm at a loss there, I'd think if they're good and being used, someone here would have info.
I'm not kickin you in the balls on the thread in any way, but you might want to post with a "drive shaft & Gen4" title, you might get someone who knows this topic better to click it, not everyone checks all threads, especially ones with general titles.
I know one guy to hit up is Steve at Vipair, he's building TT kits, and playing with Gen4 serious mods for the future, he may have a recommendation or lead on strong axles. Of course Mark J and JonB are also good sources to hit directly, again they may not click this general thread. Good luck.
Dave.