SQL Server 2012 :: How Update Works For Unique Values

Look at the following code,

Create table #test
(
id int primary key,
Name varchar(100)
)
insert into #test values (1,'John')
insert into #test values (2,'Walker')

[Code] ....

-- Query 1 :
update #test set name = 'Joney' where id = 1

-- Query 2 :
set rowcount 1
update #test set name = 'Joney' where id = 1
set rowcount 0

1. #test table have primary key & clustered index.
2. Obviously only one row will be available for an id.
3. In query 1, will the sql server look for matching rows even after it found 1 row?
4. Will query 2 really gains some performance?