Even if they dropped £100 it's worth waiting unless the card someone currently has is ruining their gaming experience, if it's just "beginning to struggle" like in the OP's case then I'd agree with Stu999 and would just wait; if you've waited 4 years then what's another 3.5 months to wait for another card you'll likely keep for another 3-4 years.
Doesn't seem like it will be 3-4 months though. If they aren't released until August/September and will be hardly available?
I guess it's a cycle.. there's always something better that you'll wait for.
My second question is whether or not a 2070S will cause my CPU to be a bottleneck?