Chewy
Thanks for the advice and the confirmation of my concerns.
I'm quite happy doing 75-85 mile rides and not feeling particularly tired/stiff and and do back to back 50-60 miles rides over a weekend. I've got a 160Km ride with 2000m of climbing planned for early April and can do 60 miles in 4 hours. So with my current training plan I feel comfortable.
This weeks issue is that I gave blood on Tuesday and it hit me really hard and I've been finding it hard to do 20 miles at tempo to brisk. I'm going out tomorrow for 40-50 miles at pace below tempo as that's how fast that group rides.