I think those terms now mean so many different things in different schools that asking for others experiences might not be all that helpful.
But, FWIW, In our school, Big Write used to mean a task unconnected to the genre we were looking at in our usual lessons, given to the children a couple of days before BW day so they could talk about it at home. Then on BW day, we would do 45 mins of VCOP warm up activities, then children would sit and write for 45 mins. We would then mark and level using the Ros Wilson criteria.
To my mind, it was a writing test every week and a chunk of time when the children weren't being taught or learning. Not all teachers gave thorough enough feedback for children to get anything out of it. The children who enjoyed writing loved it, the rest hated it. Done this way, I wouldn't see it as having any benefit if speaking and listening is your top priority - but I think you could wrap talk for writing around any approach you follow, as long as you don't get too hooked up in the 'rules' of whatever route you go down.
Now we mostly do independent writing through our topic work. We work on writing skills connected to the genre we are working towards (eg direct and reported speech, summarising, past tense and paragraphs if we will be producing a newspaper report for our topic). Long independent writing is still done in a separate BW book, but the children feel they are building up towards it and more of them look foward to haveing chance to show what they have learned. We mark it and use APP style sheets to gauge levels, which we feedback to children every half term. In UKS2, we still spring a totally unprepped long write on them and we use this to moderate our levellling.
If writing is an issue, you might want to have a look at Alan Peat. It's not all brilliant, but his idea of teaching different sentence types is, in my view, a more effective and holistic way of teaching 'good' writing than VCOP which IMVHO leads to formulaic, robotic writing.