Opencart is very useful for a serious project on it not to do - will be a big effort. Bitrix is very overrated due to the aggressive marketing, and really disgusting, once you try to do something not quite standard. Ie both not very good.
Look at some of Magento or similar projects.
Lavern_Schuppe answered on June 10th 19 at 15:20
Bitrix popularity is on the 4th place in the world, though after 3 free.
And he's imprisoned under the IMAG
instrumentation in this is more than enough.
But it's like comparing photoshop and pbrush one better n harder on the second is easier and cheaper.