Flats in general will have a stiffer feel since the widings are wide and flat. That's not true in all cases, though..just generally.
But DR Sunbeams are not flats, they are nickel rounds.
TI flats are said to be some of the less stiff flats, but I've never used them.
I recently installed a set of Chromes on one of my basses (I love rounds but wanted to have a bass with flats..just because!) and I was very surprised by the feel. They are not stiff feeling at all, especially compared to the GHS Pressurewounds I had on it before. Those are STIFF!
I've read that Lakland flats are basically GHS Precision Flats, but I don't know for sure.
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