I can comment on the subject with the benefit of first-hand experience. I used to double batch sparge and was regularly getting around 90% efficiency into the fermenter. The beers tasted pretty good to me, but I knew they could be even better. At a competition, a couple of my beers were dinged for slight tannin presence. So I started single-batch sparging and my efficiency went down to around 75% into the fermenter. My beer definitely started tasting even better and no judge has mentioned tannins since.
Having said that, you could be perfectly happy with how your beer is tasting right now. If that's the case, keep aiming for maximum efficiency. If, however, you feel your beer can improve, try reducing the amount you're sparging and see if it makes a difference. I think a lot of homebrewers have "ugly-baby syndrome" where they can't taste or admit to off-flavors in their own beers. Your buddies may be loathe to mention them either, allowing that they are even capable of discerning them. If you want to keep improving your beer and you haven't already, enter a few of the beers you think are really good into a competition. Judges vary, but you'll probably get a better idea of whether your beers contain tannins or other off-flavors.