Bridleway: you would add about 600m to your journey and it would take far longer if you didn't want to risk your ankles. You'd be risking them anyway unless you had proper walking boots.
The bit I walked the other day was flat, covered in leaves and very muddy - but it won't be wet in August of course. There is a section of about 450m where you drop down 60 or 70 m in height so the gradient there is around 1 in 7 and without the benefit of tarmac. Trees overhang from both sides, delightful on a sparkling summer day.
Through the woods there is a sort of hairpin bend to take out the worst of the steepness but you do most of the 500' (150m) height up or down on the bridleway rather than along Sid Road, so it is still a real hike. Salcombe Hill turns at 45 degrees to take out the worst of the steepest slope also, but over that section it is still betweeen 1 in 4 and 1 in 5.
Salcombe Hill is what could be called a serious hill.
On the other side of Sidmouth there is Peak Hill, rising to 167m (compare with 172m) but the steepest bit is not as severe as that on Salcombe Hill. The road is much wider too. They use Peak Hill in the Tour of Britain cycle race - only a complete nutter would try and cycle up Salcombe Hill.
Mind you, that goes for dancing in cold river water too.
Tour of Britain - video here