was this ROWS/RANGE "hint" available in 2008/R2?
also the default behaviour of over without ROWS BETWEEN UNBOUNDED PRECEDING caused a large number of reads on Worktable, after adding it it went to 0.
With ROWS BETWEEN UNBOUNDED PRECEDING
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table '#temp______________________________________________________________________________________________________________00000002A387'. Scan count 1, logical reads 673, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Without
Table 'Worktable'. Scan count 122381, logical reads 737031, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table '#temp______________________________________________________________________________________________________________00000002A387'. Scan count 1, logical reads 673, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.