In terms of the lightning claws I kinda just like the look of them lol but if power weapons are just as good then saving some points sounds better.
Good point on the khorne berserkers, I was really just using them for fluff reasons but I really like the khorne marine body conversion kit from forgeworld so that won't be a problem.
My other question is the landraider a good idea? Would beefing up the terminator squad and deep striking them in be worth looking into or would they just not have a great chance of surviving?
The only reason you'd give them twin claws is for an extra attack with 2 specialty weapons for cheap, otherwise a power(or chain)fist and lightning claw is better, allows you to choose between x2str (armourbane with a chainfist) or marine shredding with +1 attack, as it is in a land raider (which is a good idea, expensive, but good) you'll still have a great number of attacks with MoK, so regular power weapons should do the trick. You can if you want, drop the cultists and beef up the Termis with fists and claws or combi-meltas and power weapons, but i think with standard combi-bolters and power weapons they will still be feared. If you deepstrike them, you have to have them exposed for a turn before you can move, and that's usually a bad idea. Unless they're a suicide unit.