Yeah...I think that's just a little much unless you do it very slowly...30% would be better and than get in the habit of doing it regularly. I have pretty much the same set up as you, 65 gallon bowfront with a 30 gallon sump/fuge. I do a 5 gallon water change daily...it's easy as pie...5 gallons out, 5 in and I'm done. I keep a water storage tank filled with mixed saltwater, a pump and heater. I have a Maxi-jet 1200 powerhead with some tubing attached plugged into a powerstrip (easy on and off) I blow any gunk off the rocks with a turkey baster and as it makes its was to the sump, I put the powerhead in the sump, turn it on with the power strip and pump out 5 gallons of funky water. Turn off (that's where the power strip is handy...no yanking on plugs..just push a button) Pull out the Maxi, put it in the clean water and pump 5 clean gallons back in. This means I am changing 35 gallons of water a week, but it only takes a couple of minutes a day.
I believe the NUMBER 1 thing we can do for our tanks to keep them pristine and the colors bright is regular, small, consistent water changes. Since I started doing this the colors on all my corals, SPS, LPS, zoas, etc have exploded...so has growth. And instead of having to block out an hour or so to get things done, it takes about 5 to 10 minutes...everyone can spare 5 or 10 minutes.
Just make sure you check the salinity of the water so that there is no evaporation in the saltwater holding tank and you pump in the water at a higher salt concentration. Add a little fresh RO/DI water or whatever you use to get things matched up.
If it's hard to do or time consuming, we put it off...a couple of minutes a day is easy and your tank will love you for it.