12 on the main, 8 on the traveller, 10 on the heady & poled headsail sheets. We were on 12's but works just as well on 10's, although when it gets up around 20-30 it needs 4 wraps to stop slipping. Mine are non tailing old school Barlows with a 150% #1 and 135% #2 headsails.

I replaced my 12mm main sheet with 10mm and the ease of use because of the reduced friction( I guess) was gobb smacking, that being said its only 23m2 ish sail with a 4:1 purchase

Dexport said..
Strength-wise you'll be fine with 8m, just comes down to ease of handling and what your winches are geared towards. Headsail sheets that you're handling all the time are nicer if a bit thicker, means less blisters.

blisters are never an issue, always use gloves. I think the 8s slide easier through the fittings. I wonder if that extra thickness helps a bit with longevity

On my 28 most halyards are 8mm spectra, spinnaker halyards 10mm db, spinnaker sheet 8mm db, barber hauler 5mm db, Genoa 10mm db, main traveller 8mm db, boom traveller 10mm db, boom uphaul 8mm spectra, main preventer 8mm db, reef line and outhaul 8mm db, cutter halyard 10mm db, sheet 10mm db, running back stays 8mm spectra, back stay adj. 8mm dynema.
It works fine at steady 35 knots.

Hort said..
G'day, as dexport says strength isn't normally an issue with modern ropes it just comes down to handling.
We ran 6mm & 8mm sheets on everything on a Sayer 12m full carbon race boat, no problems just wear gloves...

G'day Hort, what boat?
Seabreezy, I run a max of 10mm on a 40'. Smallest sizes are the spinnaker tweakers at 6mm. For your sheets, make sure they''re big enough to hold comfortably and small enough not to foul your self tailor /deck jammers/cleats etc. Too big a sheet on a self tailor will guarantee it pops out when you least want it to.
And always yes to gloves, and make sure they are in good nick. .
A good mate just upgraded from a Benny 40.7 to a H&H 42, on its first/second sail a month ago his hand slipped of the pedestal, and falling he grabbed the mainsheet just as the trimmer was easing. Result was his index finger went into the turning block and took it off clean. They re-attached it, but it failed to graft and they amputated this week.
Easy to do. I didn't quite lock the traveller last Sunday, and even holding tension on it, the dyneema slipped through my old gloves, shredding the gloves and a couple of layers of skin.
Still can't hold a bloody pen.

Of course the cost of hardware rises exponentially with the size of rope. 10mm and 12mm is good size for me.

Hort said..
Shaggy, the boat was Wasabi
built for & raced in Melbourne to Osaka

Cool boat. Melbourne to Osaka....now that would be an achievement.

we run 5 mm dynex on main and jib halyard the main halyard goes to original captive wire winch jib halyard is spliced into 3 strand polyester as atail for handaling

shaggy - thanks, I have learnt to be careful around ropes/sheets when my mum's finger was taken off by our german sheppard held on a leash.
plus, if you do not realise how much a nylon rope can burn your hand, you are a fool. As my instructor use to say it: wear gloves, you only have one skin and the rope is stronger, that is why you use it..

Twodogs - I do not see the difference between racing and cruising. If a rope handles harder because it jams due it's larger size, why is that better for cruising? I had 12mm on the jib before and it would barely go through anything. Yes, it was easier to hold, but because it was larger, it started to chafe/wear out sooner.

Jackthe - there is only 10c difference between a size 8 and 10 I think and 100kg in strength

rumblefish - I tend to agree, but rather the size, maybe the frequency of swapping it out for a new one matters more?

I think 10mm will suffice. But there is a difference between rope nd rope. Where do you get your ropes from, Whittworths?