Bitcoin arbitrage?

Quick example:
We start with a 20k roll.
We put 10k into Exchange 1
We put 10k into Exchange 2 and we turn it into BTC at a 4300 price => 2.325581395 BTC
We look for a difference of 100$ in prices between the 2 exchanges. 
In theory we should have around 200$ profit each time that happens. However after studying this in excel it's not that straight forward because we deal with 2 currencies:

So we have 
10000 $ and 2.325581395 BTC

We find an opportunity at 4600 vs 4700.
So we now have 2.168478261 BTC and 10902.90698 $
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Well...
if we calculate that at a 4650 price, we'd have a roll of 20986.33089 $  
If we did a hold & pray full start amount in BTC we'd have 21627.90698 $

if we calculate that at a 4850 price, we'd have a roll of 21420.02654 $
If we did a hold & pray we'd have 22558.13953 $

if we calculate that at a 4300 price, we'd have a roll of 20227.3635 $
If we did a hold & pray we'd have 20000 $ (breakeven)

if we calculate that at a 4000 price, we'd have a roll of 19576.82002 $
If we did a hold & pray we'd have 18604.65116 $

The current assumption is the price will keep going up.

It is however unlikely for it to go up from 4.3k to 6k overnight - especially since it dropped twice from 4.9k to 4.1k then from 4.7k to 4.1k.
It's realistic to expect such battlefield levels to happen often during this assumed rise in pricing making arbitrage significantly more profitable than holding.
The price will just not rise 300$ on average for every 1 arbitrage that we find. There should be plenty of back & forth action especially with the price being high now.

Realistic outcome: we find 4 arbitrages like that per month for around 1k profit
That is a conservative estimation, for example this week I saw a 200$ difference in pricing for good minutes, that alone would've made 800$ in profits.
Optimistic outcome: we do about 2k profit.

ROI : 
realistic 5% per month / 80% yearly
optimistic: 10% per month / 200% yearly

Sports arbitrage would have a higher ROI but can be done only up to a certain limit due to max bet sizes. There is no real max bet here on an arbitrage, we could roll the entire amount.

When doing arbitrage we are basically holding half of it at all times too so the final profit depends on BTC pricing.