Dramatic decrease in SQL Azure performance after scaling to new edition

Yesterday, we scaled one of our databases in Azure from the old Business edition to the new Standard one (S2).

Since then, it has been behaving rather erratically.

We have a relatively simple table called dbo.Asset. On it, there is a column called ContentSetId which is of type integer. This column is also covered by an index:

CREATE NONCLUSTERED INDEX [IX_Asset_ContentSet] ON [dbo].[Asset]
(
    [ContentSetId] ASC
)

The table contains around 2 million records.

The below query took 36 seconds to run the first time, but 0 seconds on subsequent runs. We are seeing similar behaviour in other queries too, whereby they can take upwards of a minute to return under 1000 rows, but subsequent runs are much, much quicker.

SELECT TOP 100 * FROM dbo.Asset WHERE ContentSetId = 3

As stated above, we have only noticed this behaviour occurring since changing from the business edition to the new standard s2 one.

Any suggestions would be very welcome!

I conducted a series of performance tests against the new service tiers (as mentioned by another poster above).

I tested I/O rates back in July and have now also tested the memory (i.e. max buffer pool size) in each tier:
http://cbailiss.wordpress.com/2014/11/11/azure-sql-database-memory-limits-by-service-tier/

(I was going to add this as a comment on dark_perfect's comment above, but on this site I don't have enough reputation to add comments yet).

StackExchange Database Administrators Q#80262, answer score: 5