You are slow. Sometimes 365 not enough too.

@Naggzu 330 should stick in Gold 3 by end of week, 340+ in G4 by end of week. 

lol so by your logic you need to arbiter to be @330 speed to hit gold 3. Yet you need to get to g4 to obtain arbiter in the first place. Let alone gear her up to 330 speed to be in a rank below receiving her.

I would not like to be a player trying to get arbiter right now, it must be incredibly frustrating

You don't need arbiter to get to gold4  at  all,  much  less  the  stated  speed.    He's  saying  IFF  u  use  Arbiter,  these  are  her  average  speed  in  G4.

I'm not really sure what your point is here, or why you're putting words in my mouth.

OP asked what speed his (reading is important) Arbiter would need to be and I answered what I know to be a safe answer. I know it was possible to stay in Gold 3 very recently with a ~315 speed Arbiter, but that perhaps required more frequent refreshes/selective matchup choices. There can be other factors at play such as specific gear sets, the rest of your comp, so on and so forth. 

Speed is a linear strategy that has been attainable for players for years now through gear and glyphs, thus the speed cap is higher. There are other ways to go about climbing Gold (or higher) arena than just being the fastest, but yes, things are difficult right now.

This is pretty accurate. My Arbiter is only 330 in high g4/g5 but I also have other champions that allow me to be a little punk and stay there. Tormin, Hegemon, lyssandra (as a second booster against slow teams), and Soulless. 

Getting to G4 can be done with slower speed, but STAYING there requires at least the speeds Dthorne said.