;with cte as
(
	select 'W1000' as KeyField union all
	select 'W9999' union all
	select 'W10000'
)

select KeyField 
from cte
order by KeyField

;with cte as
(
	select 'W1000' as KeyField union all
	select 'W9999' union all
	select 'W10000'
)

select KeyField 
from cte
order by LEFT(KeyField, 1), CAST(RIGHT(KeyField, LEN(KeyField)-1) AS BIGINT)

;WITH cte as (
	    select 'W1000' as KeyField union all
	    select 'W9999' union all
	    select 'W10000'),
    cte2 AS (
        SELECT MaxN=MAX(CAST(RIGHT(KeyField, LEN(KeyField)-1) AS BIGINT))
        FROM cte),
    MyNewData (n) AS (
        SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3)
--INSERT INTO Table (KeyField)
SELECT 'W' + CAST(
    n + (SELECT MaxN FROM cte2) -- Use ROW_NUMBER() instead of n if needed 
    AS VARCHAR(19)) 
FROM MyNewData