Looking at their current positions in the table, managers, squads and ability to spend in January, I think that Wolves, Cardiff, Derby and Villa are all nailed on for top 6 places, and that Wolves are nailed on Champions. It probably leaves 2 other slots for about 10 clubs to aim for.
Bristol City currently sit 3rd. Lee Johnson has had a (very) bad spell in almost every season he's been a manager, but there seems to be a lot more steel about that Bristol City side now. I wouldn't be surprised if they did drop off and still have a solid top 10 finish, but at this stage they are flying and show no sign of letting up. They have the finances to go big in January too, in order to help maintain their position.
Also, there are some sides that can't be ruled out, who are seriously underachieving at the moment, whilst still being not too far off 6th as it stands. I'd expect the likes of Boro, Wednesday and Fulham to eventually start closing in. Possibly even Reading too who look to be playing well again but the lack of a big money striker signing they craved in the summer has hurt them.
The clutch of ourselves, Ipswich, Leeds, Sheffield United and Forest will also fancy their chances too.
It should be an interesting next couple of months, seeing if certain teams can maintain their challenges and what they do in the market.