Agouti,
I run a similar set-up, 260 watts (50% 10k, and 50% actinic 03) over a 55, and it is tons of light for certain corals (softies and LPS corals). They are not hallides, they are PC lights.
So the guy at your LFS was accurate...to a degree...it is good enough for a reef, but not good enough for certain high light corals. You could easily keep softies, and most LPS etc.
BUT, it is NOT enough light for SPS corals or for most clams...just not enough light, and not intense enough.
Also, I am not sure how mature your tank is, but you would want to avoid clams until you had a pretty mature tank and have stable water parameters.
HTH
Stewart