Newcastle have proved that they can compete favorably with other top flight teams in the English Premier league. The played a 3-3 draw against Manchester City, 0-0 draw with Manchester United. They beat Tottenham 2-1 and won Chelsea 1-0. How else do you want them to prove their ability. Newcastle have one of the best teams currently and the management of the club has the financial power to attract and buy more quality players.
I believe Newcastle even have a better chance of performing better than other top four clubs because they are not competing for any continental trophy which means that their players can just focus on winning the premiership.
Manchester City and Manchester United didn't lose to Newcastle, they only drew. Chelsea and Tottenham are the two teams they managed to overthrow, but not Arsenal and Liverpool. So I don't think Newcastle have been better, but their form so far has been good.
You can't expect much from Newcastle anyway, so even if they play well and avoid more defeats, there is always a high risk of including them in your betting slip. I know that, and it means they are not believed enough to be able to keep their performance.
Currently, Newcastle's winning streak is far above Chelsea's. I don't think one will prefer Chelsea above Newcastle when it comes to betting slips. If I were in such a position I will choose Newcastle as I believe many others will.
Speaking about being able to keep the position, I don't. Think Newcastle will be weak in the remaining half of the season because currently, the team also has big hands in the transfer market even with a stable team, I believe they will be continuously bent on doing.