Good going Frisky,
I have a similar arrangement, three days a week, rest days in between, drive the other two. That's for a 20 mile trip each way on a fairly flat route.
I have become accustomed to it now, but still get DOMs if a cane it, looking for a PB, or swap to a hilly route off the main road. I adapted within a couple of months.
The reason I started was to save petrol when it went up to £1:20 /litre. I tried the whole week but became prone to injury, saddle sores, and spending what I would have saved, on food. I found it almost impossible to eat enough to get through the whole week.
I guess the compromise is working well for now.
Biscuit