Actually Colin, I am toying with a similar idea for the summer. A ride down to my dad’s house in Cwmbran, near Newport, south Wales. It's around 160 miles but a little climbing as I pass near Abergavenny (tries desperately to remember the name of the hill range in that area....). I too was planning on a one day big hit strategy with an escape overnight stop planned for around the 110-120 mile mark for if it didn't work out. There has to be an enormous sense of achievement from completing something on this scale?
The Black Mountains? 
I thought about doing my trip for years but didn't feel fit enough until 2007. When I finally did the ride, I coped with it really well and I did feel pretty pleased with myself afterwards. I enjoyed it so much that I rode back a week later rather than coming back by train.
Bikely shows it as 126 miles but I haven't followed all the little twists and turns in the roads, and I also took a wrong turn when for some stupid reason I stopped following my GPS's instructions and tried to improvise a new end to the route! Somebody had turned a road sign round and I almost ended up in Nuneaton instead of Coventry. Including stops, it took me 12 hrs 45 minutes to do 141 miles.
On the way home, I discovered that Snake Pass was closed for resurfacing. Normally, I'd take a chance and try and sneak by, but it is an awfully long way to ride up there and then have to come back down again if it
was impassable! I rode to Holmfirth via Strines Moor instead, a route I actually preferred to the way I'd ridden out. I was doubly chuffed that I managed to ride up the 25% section of Ewden Bank with panniers on my bike!
It sounds as though your 160-miler has less climbing than my 141 miler and you are at least as fit as I was in 2007, so I say -
go for it! 
Choose a day near the Summer Solstice to give yourself plenty of daylight hours and hope for pleasant warm conditions. (My ride took place on June 28th in the miserable 2007 summer. I wore arm and leg warmers plus a gilet and overshoes. When I was descending off Snake Pass towards Ladybower, I got so chilled that I had to stop and add a windtop!)
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