If in the last two seasons, maybe I would also say that arsenal will beating westham, but for this season, to be honest I'm not sure if arsenal will be able to easily beat westham, this season westham which is handled by moyes has turned into a pretty solid team and very hard to beat, just look at how easily westham beat chelsea and liverpool which is a strong club this season, in my opinion, arsenal will be the next victim of westham.
West Ham is very strong and Arsenal can not underestimate The Hammers. They are making us surprised in this season and their match will be interesting because it can be a broken time for them. When their good streak ends, their bad streak will start. Who will get a start of bad streak?
I hope Arsenal will get one position in top 6 of Premier League and it will help them to enjoy standing on top of table. It can be booster for their next season when they can become stronger and fight for higher targets.
West Ham will obviously be a big threat to Arsenal. It's hard to beat West Ham with them in such good form. Even West Ham can be a dark horse in the current League. Considering the competition between the top 3 clubs, the focus should be on chasing the top clubs. While West Ham can certainly take advantage of this situation to move under it by dropping Arsenal or Man United though.