R33 GTR new tyres - standard wheels

[the beast]

Running standard set-up 17s with 245/45 tyres -
need to replace all 4 and curious about changing tyre size to say 255/40 which seems to be possible (and tyres are cheaper!)

Anyone can tell me how this affects car? In terms of handling, grip, comfort and also speedo readings?

Am I better off sticking to original size or will I get some performance benefit?

Thanks