125mi London to Brighton route - sanity check :)

Yes, you did do that bit from mile 91-97, great minds!

I see what you mean about the crossing at mile 92, Burnthouse Lane.  I haven't ridden it, but the Google maps car made it so you should be ok.  There are two more small roads just east of there, I may have been thinking of them.

Great challenge by the way!  Don't tell the off road folks, but the way they are going, the Downslink is very, very dull. I've done it for charity a few times, and can't face it again! 

I live down this way, Stan's is good.  

You've missed a lovely bit at mile 97; Doomsday Green to Bucks Head goes through the Hammerponds which are lovely and well worth checking out.  At mile 92 when you cross the main road, I don't know if you can ride down there; it might be private or un-made.  I would follow the road round to the left just after mile 91, and go to Maplehurst.  Then either go left to Copsale and Sedgewick and then up to Doomsday Green, or carry on through Nuthurst (nice pub if you need an extra stop) but that will give you a mile or two on an A road, but it isn't that busy.

The bit from mile 78 to 87 is lovely.

If it is too easy, you're very close to the toughest hill in the area, Barhatch Lane near Cranleigh...

It looks like you've picked a nice bike-friendly route and I'm sure you've already done it, but I often look at Google Streetview to reccy new routes.  It's great for seeing whether lanes are dark, light, narrow, wide, rutted or well paved (as well as previewing possibly tricky junctions if necessary).

Say hi to the ducks by the pond between miles 59-60, they're not shy in coming to say hello if you stop for a snack...

https://goo.gl/photos/63DLanP7ME9thjaF8

https://goo.gl/photos/4tcWRNVRrbGPH52Y9

I was going to reply last night, but after looking at the route, I had to go and have a lie down.

Enjoy the ride.

If you have not done so yet, take a look at the bits of the route you are most unsure about on Google Streetview.

Because I don't use GPS navigation on my rides (only GPS logging - Edge 500), I typically recce new routes via Google Streetview before I ride them.  Helps me remember which way to turn at each junction, but also helps avoid potential route clangers [cultural aside - I don't mean the small knitted creatures...!]

I did this when planning a new route to cycle the 40 miles from home to my parents house at the weekend.  There were a number of places where I changed the route because I did not like what I saw on streetview.

Good luck - your idea sounds better than the BHF ride!  I did it in 2007 with a team from work, and starting at ~11am, we spent the majority of the first 10 miles or so walking with our bikes because there were far too many entrants on the road at that time.  Think I would only consider London-Brighton BHF ride in the future if I could be in one of the very earliest start groups with enough clear road to allow me to be in Brighton for breakfast.

I don't know that area at all, but I find the Strava heat map useful for getting a feel for which roads are popular with riders in a new area: http://labs.strava.com/heatmap

Can't see anything wrong about route south of Leith apart from twists and turns..and stans bike shack is a great shout for coffee and cake at partridge green

stop for coffee at stan's just south of partridge green (134.5km). they do a good salted caramel brownee