new tires, new sizes

I'm considering upsizing my tires for a slightly sportier/stiffer feel with minimal affect on mileage. I have been spending hours of my life reading through the vast sea of tire threads, and I have not found any hard facts about how the mileage is affected. I understand the concept of lrr, revs per mile, and metric tire sizing, and its affect on speedometer reading. Most people are using language like, "Mileage will take a hit" or "you'll see a drop in mileage"etc. I'm looking for any exact mileage data based on first-hand experience when switching from stock 185/65r15 to 195/60r15 or 205/60r15. I just drove 300 miles last night on my 2005 prius, and averaged 47.5 mpg on cheap bald hankook 185/65r15s and noisy worn-out front struts (that I'll be replacing soon). Speeds were divided almost equally between 55mph and 70mph roads, and I passed through two towns with some stop-and-go. I'm hoping to improve cornering/handling while keeping the mileage around the 45mpgs. One or two mph difference on the speedo is not an issue for me. Also, any first-hand people out there have issues with hydroplaning on these upsizes? We see little/no snow here in NC, but we get plenty of heavy rains. Thanks for any time you could put into a response!

 

Thanks for the response! The new struts are sitting in the garage, and I'm waiting for some spring idolaters from toyota. All those things you mentioned are in the works. I do remember what the car handling felt like at about 15000 miles, which wasn't bad overall. But, it's always had a ton of body roll.