Ive just replied to one of your other posts and didnt see this one first.
Whilst BT do not officially cap - they are indeed throttling connections during peak time. From what Ive seen its on most protocols and not just p2p
Sky... well although they arent capping or throttling like BT are doing, Im not too sure if some sky exchanges are perhaps reaching saturation.
You may well be ok on sky - many are.. but after observation of a
sky connection on my own exchange I'm not too sure what the future has in store.
I could be being pessimistic... but many will recall that this exchange was the first exchange in the UK which BT admitted suffered from exchange congestion.. and has always had a bit of a problem... hence why I wonder whats going to happen in the future.
If you are in a position to migrate with a MAC, then if I were you I'd look at ISPs that have a one month contract.. then if things do go wrong at least you can get out and move on elsewhere.