Hi
Since water weighs over 8 pounds to the gallon plus the weight of the tank and gravel?? Since nothing is as important as the stand . and the most difficult to change once setup .I'd do some reinforcing..
Be sure to get it level in both directions shim the stand not the tank. and definitely use materials that won't absorb water. Save you tons of problems down the road. Those flimsy stands are exactly that. gary
Those flimsy stand you mention are exactly that lol.

If it's looks heavier than the stands it probably is, you should be ok. Granite sounds expensive since it will be mostly covered by the tank and can't be seen. Make sure its level. Also i would recommend real wood not a laminate. Water spill on it could cause swelling and rotting. Use regular wood, it should have a frame and poluurethane finish.