Part of this answer will be defined by your wheels, how wide are they? Flo cycling did some testing on this using the rule of 105 (rim should be 105% of tire), they found that with their wheels 25c was aerodynamically faster (roughly 104% vs 97%) going to 28c had lower rolling resistance. The combined difference had 28c barely edge things out, with a difference of .09w on the least aero rim to .43w on their most aero rim. That would suggest that wider still would have had enough aero disadvantage to not be worth it though I wonder if it also due to the tire not being a less optimal shape when going wider which could effect the amount of reduced rolling resistance. Course their test might be old enough 30c wasn't popular yet. The result is that I'd very much base it on your wheels. If you have an older, narrower rim and you'd drop somewhere below that 95% rim width, I'd be disinclined; if you have newer, wider rims I'd go wider if the frame can handle it.