Azure Virtual Machine Disk IOPS Performance vs AWS

I have a MongoDB replica set with approx. 200GB of data.

This currently exists in AWS on two medium.m3 instances (1 core, 3.7GB). I have a requirement to move this to Azure A2 instances (2 core, 3.5GB), however I am concerned about the performance.

In AWS I have a single disk per machine, 220GB SSD through EBS which delivers 660IOPS (or whatever this means in AWS speak).

According to Azure, I should get 500 IOPS per disk, so I thought performance would be comparable, however here are the results of mongoperf on Azure:

Azure mongoperf Output:
{ nThreads: 2, fileSizeMB: 1000, r: true }
creating test file size:1000MB ...
testing...
optoins:{ nThreads: 2, fileSizeMB: 1000, r: true }
wthr 2
new thread, total running : 1
read:1 write:0
64 ops/sec 0 MB/sec
82 ops/sec 0 MB/sec
85 ops/sec 0 MB/sec
111 ops/sec 0 MB/sec
95 ops/sec 0 MB/sec
106 ops/sec 0 MB/sec
96 ops/sec 0 MB/sec
112 ops/sec 0 MB/sec
new thread, total running : 2
read:1 write:0
188 ops/sec 0 MB/sec
195 ops/sec 0 MB/sec
223 ops/sec 0 MB/sec
137 ops/sec 0 MB/sec
222 ops/sec 0 MB/sec
212 ops/sec 0 MB/sec
200 ops/sec 0 MB/sec

Whilst my AWS medium.m3 instances perform totally different:

AWS mongoperf Output:
{ nThreads: 2, fileSizeMB: 1000, r: true }
creating test file size:1000MB ...
testing...
optoins:{ nThreads: 2, fileSizeMB: 1000, r: true }
wthr 2
new thread, total running : 1
read:1 write:0
3149 ops/sec 12 MB/sec
3169 ops/sec 12 MB/sec
3071 ops/sec 11 MB/sec
3044 ops/sec 11 MB/sec
2688 ops/sec 10 MB/sec
2880 ops/sec 11 MB/sec
3039 ops/sec 11 MB/sec
3020 ops/sec 11 MB/sec
new thread, total running : 2
read:1 write:0
3133 ops/sec 12 MB/sec
3044 ops/sec 11 MB/sec
3052 ops/sec 11 MB/sec
3016 ops/sec 11 MB/sec
2928 ops/sec 11 MB/sec
3041 ops/sec 11 MB/sec
3061 ops/sec 11 MB/sec
3025 ops/sec 11 MB/sec

How can I achieve the same performance through Azure as I do through AWS? I have looked at the D* instances which provide local SSD storage of 500GB, however these disks are ephemeral and so no good for hosting my database.