Watch the Tour of Britain highlights on ITV4 tonight to see what the most obvious route from Windermere to Kendall is like! (Windermere, Bowness, B5284, Kendall.) The B5284 looks like it would be great in dry, sunny conditions in light traffic, but a nightmare if it were raining and busy!
If I were going to ride from Penrith to Kendall, I would probably miss the first bit of the A592 and take the B5320 instead from Eamont Bridge to Waterfoot on the A592.
Do the long, hard slog over the Kirkstone Pass, and then begin the long descent towards Windermere.
I would choose to bypass the obvious route via Bowness mentioned above. Instead, I would turn right left off the A592 at Longmire and ride over the hill instead of continuing down to the town. Turn left onto the cyclepath next to the A591 at Ings and ride to Staveley. Call in at the cafe at the brewery next to the big Wheelbase store there.
After a cafe stop, follow the cycleway to Burneside.
From Burneside you could choose to drop down into Kendall, and on to Oxenholme OR (the harder way, which I would prefer) climb up the hill to Laverock Bridge, cross the A685, stay high and work round to Singleton Park, cross the A684 and drop down into Oxenholme.
I'll plot a profile of my suggested route ... do you prefer miles/feet, or kms/metres?