Supercharging daily will indeed have a negative impact. Do you have a garage? Do you have the ability to purchase and install a level 2 charger? If so, I'd have zero concerns. If the 75D @ 80-90% gets you enough to handle your business on a daily basis I think you're going to be just fine if you have a home charger installed.
When I purchased my Model S a couple of years ago it created a domino effect in my family. My dad, my sister, my cousins....everyone made the switch to EV's (all Tesla's) shortly after experiencing my car. 1 of my cousins lives in a condo and doesn't have the ability to install a level 2 charger. He found a mint late 2014 build P85 and supercharges 1-2 times weekly. In the 2 years he's owned it his stated range @ 100% has dropped 2 miles. (The guess-o-meter display isn't the accurate way to track degradation, but it's what I have to go off of on his car).
Someone replied to one of my earlier replies here with the fact that only Tesla has the real data on such things, and this is correct. All I have to go on are my personal experiences. You should also factor in the cold weather range loss if you live in an area where that's a reality. Some of these other, more well versed TMC members might be able to speak on the expected cold weather loss better then myself. The P85 example I'm speaking of is located in Connecticut and he sees ~ 15-20% range loss when it dips below freezing.
Putting your hands on both cars is indeed the smart play!