Anybody know would the blade rotating speed on a D125 slow down as I lower the mower deck?

I recently purchased a 2010 john deere x500 garden tractor with a 48" mower deck, I Am interested in purchasing the best possible mulching blades, I do not have a mulching kit or a bagger, I cut about one acre, and at times have quite a bit of leaves, I would like a blade that will really cut up...

I'm in the market for some new ones and was thinking about the Oregon Gator blades. I remember reading here somewhere that they're a fraction longer than OEM and they may have a tendency to hit one another. Please help with recommendations. Thanks