Summing Only The Greatest 5 Values In Each Group

Hello,
Here's one way to sum only the top 5 (greatest 5) values per group.
I assume there is a table called IdValues that contains two columns: id int, value int.

declare @lastId int
declare @value int
declare @count int
declare @idList varchar(5000)
declare @valuelist varchar(5000)
set @count=0
set @lastId = -1
set @value = 0
set @idList=''
set @valuelist=''

select
@count=(case when @lastId<>id then 1 else @count+1 end),
@value=(case when @lastId<>id then value when @count<=5 then @value+value else @value end),
@idList=(case when @lastId<>id then cast(id as varchar)+','+@idList else @idList end),
@valuelist=(case when @lastId<>id then cast(@value as varchar)+','+@valuelist else cast(@value as varchar)+','+right(@valuelist,len(@valuelist)-charindex(',',@valuelist)) end),
@lastId=id
from IdValues
order by id desc, value desc

select @idList,@valuelist

It's a funny approach. I'd be interested to see a better method. In MySQL it is possible to do this much better and have it produce an actual resultset (since MySQL allows you to assign variables and product a resultset in the same query).

I also noticed something interesting. If you do any operation on the order-by columns, the query doesn't work. For example, if I do:
order by id+0 desc, value desc
something funny happens and you only get one id and one value in the list variables. Maybe someone else who actually some idea of how SQL Server works can explain this.

Thanks,
Thomas