340 whiplash vs. voodoo vs. thumper

Well, I'm not a believer in the thumper line and I don't use them. But - considering Comp products in your post I'd go with these three in this order:
1. Comp - XE268H: It performs very well and can run a single spring (with damper) so the whole thing is "drop in. I personally own three of this cam family and have run more than 10 in customers' engines.
2. Huges - HEH1523AL: I'm not a fan of Hughes products. Not ebcause they don;t work - they do - but because they are best at marketing and self promotion, and worst at customer service. However - again, this cam uses a single spring with damper and the whole package is drop in. So it's #2. I don't think it will make any more power than the XE268.
3. Lunati - 10200703: This is slightly larger than the XE and IMO will make the most power. But - it requires dual valve springs per Lunati - so the heads need to be taken off and the guides and spring seats cut for them. They also tend to be a little more pricey. So it's #3 on the list.

Any of these cams should make around 350hp in the package you have, the Lunati might make a little more depending.