I have a ten year old system. It's a noticeable difference in areas where I've done heavy terraforming, but it's not unplayable. It drops from my normal 40-60 to around 30 with some heavy (but very brief) dips below 20.

The real fun starts if I go from an area where the terraforming hasn't loaded in yet to the area it's in. Once I'm in the area (either having been there or teleporting in), it's fine, but it's *really* bad when I'm approaching the area and it's hitting the LoD threshold. Then it drops to basically commodore 64 loading.