This is for 5 gallons, right? That sounds close to the rate that I use in the mash, and I have relatively low bicarbonates in my water (around 60ppm). What is your water like? I use half of what you plan to in the sparge water to adjust it to pH 5.5... If you need that much acid to bring your sparge water down to the correct pH, you may be able to use more in the mash.
The other alternative is to reduce the pH more in the kettle. Although it doesn't sound Reinheitsgebot-kosher to do that, Kao has talked about it and actually mentioned that a higher mash pH can favor the enzymes that make a more attenuative wort. If you aim for 5.4 or 5.5 in the mash you should be fine, but you can reduce it to 5.2 with acid (or perhaps, a decoction) after that.
At any rate, I think you current additions should be fine. Definitely try to measure the pH if you can. It's not necessary to do every time, but I find it very useful to calibrated against the spreadsheet estimates.