I investigated performance of Umbraco.
I created business entities by C# and compared a response time of the site pages (I not opened page with viewing business entities). After data generation and before comparing I restarted the site on IIS.
All my business entities refer to an only one document type with 4 properties (title, price, is sale, description [10 words]).

My results:
Version 4.72, Stable:
After adding 25 000 business entities the site could not be started (timeout error).

Version 5.1 CMS (RC) Apr 19 2012, Beta:
After approximately 2 200 business entities the site crashed with the error: “The incoming tabular data stream (TDS) remote procedure call (RPC) protocol stream is incorrect. Too many parameters were provided in this RPC request”.
The admin part and public part were not opened.

Version 5.1 CMS Apr 27 2012, Stable:
After approximately... 100 (a hundred only) business entities the site crashed with some LINQ error on rendering view. The admin part and public part were not opened.

My question:
Does the "Umbraco” team plan to improve performance?
What result can we expect and when?

My choice of CMS will depend on your answers on this questions.
I really like “Umbraco”, but its performance is the weak link.

P.S. Code from adding business entities (v5.1):
Hive.Cms().NewRevision("Toy-generated-" + num, "Toy-generated-" + Guid.NewGuid(), "plasticToy")
.SetParent(parentContentId)
.SetValue("aName", "Toy generated E" + num)
.SetValue("aDescription", descriptionGenerator.Next(10))
.SetValue("aSale", (DateTime.Now.Ticks % 5 == 0))
.SetValue("aPrice", DateTime.Now.Second)
.Publish()
.Commit();