BitBlt is rich enough (color maps or direct color components, depths, endianness) to make this unpredictable by simply analyzing sender chain in source code (it's too deep and convoluted).
The best way is to try it, but then one must choose a benchmark, and here again it is a difficult decision, because maybe you didn't bench a path that some other use intensively, how to guess without above analysis?
I saw those un-necessary mismatch while analyzing Graphics code...
By a principle of economy, I suggest to remove them.
Simplifying code a little bit is already a win.
Then, les petits ruisseaux font les grandes rivi�res, cumulated micro optimizations may pay.