I'd say the bikers would be a better choice, much more mobile and the Tougness as well as the turbo-boost will make them draw fire. Plus you can set them up the same. I'd also give the plague marine squads (at least one, i'd go for two) meltas.
Consider stripping the termies of champion status, and seeing how many points that leaves you with... If you can, fit in a havoc squad in a rhino w/ 4 meltas and a power fist! Just nasty there!
And D_K, I hate to say it, but in such a list as Steve has, the land raider wouldn't be of much aid. At such a high toughness as his base troop is, getting shot and wounded will be hellaciously hard, and he STILL has the 3+ save to fall back on in most cases! More bodies and options (weaponry wise) is the way to go.
I do agree through... Bikers and anti tanker.. I love raptors, but they just don't seem to fit papa nurgle.