Why do you want to sail? If it's a delivery with a time limit you'd go in conditions you'd not take the wife and kids out in.
To answer your question. In my 25ft sloop a F7 on the nose in the Solent isn't the end of the world for me and some mates or if I'm on my own. It'd be a bit tedious in open water but F7 up wind is do-able if the seas are formed by the wind rather than a hangover from the previous F10.
Some of the other boats I sail are a bit bigger so I'll push it a bit further. In heavy weather you can't beat BIG. Big strong crew and big strong boat will do the job everytime.
Where you are in relation to the wind and fetch is important. I often take crews of beginers out in big winds and seas but I like it to be a reach with a sheltering shore to windward.
When is a consideration. I'm always amazed at the tales of big winds my non sailing mates sail in in the Greek Isles. I think a F5/6 is a reasonable sailing wind with the sun shining but mid channel in February it's a different situation.
With whom are you sailing. If it's the family they might be complete storm hounds but I'd rather do my heavy weather sailing with a crew of hardcase strangers really.
How do you judge conditions. From the forecast? I'm firmly in the go and have a look camp.
We chartered an Achillies 24, many years ago, from a bloke in Poole. We wanted an early start so we moored on the outside of a raft of boats at Town Quay. That was the week before havoc was wreaked on the Fastnet race. It was quite blustery. We sailed as far as Chichester & back calling at many ports in between, and moored, inbound, to the same trot. Two of them had been to Studland and reckoned not many of the others had moved all week. That indicates to me that conditions are less about wind a sea than about a whole raft of social considerations as well.
It all depends, I did a YM exam in a 10, and had a lovely long run from Dover to Denmark in a 9/10 and surfing a Global challenge boat in 55 kts was fun but I have also been sick as a dog in a 4 when wind and tide disagreed.
Last year I seriously looked a buying a 2nd hand RNLI boat just so I could go out in some really horrible stuff.
I go out in forecast conditions that are safe for the passage I'm making, bearing in mind the capabilities of the boat i'm in and its crew. I did my day skipper in the solent in a storm, by intention, and have been caught out unintentionally in an unforecast Channel violent storm.
But a few weeks ago I left my yacht in Cherbourg because of a forecast 6-7 and didn't come back on the ferry until i had a forecast of 4-5 - then fed the fish all night 'cos the wind veered, went up and set up one of those lovely chops........
The next weekend was 2-3 up the chuff all the way back to the Walton Backwaters.
I'd take my VIPs out in a seven but leave the wife behind after a five. Why? they have two hands whereas She Who Must Be Obeyed only has one!
You have to understand all the limits of the boats and the crews then stay inside them.
I went out this afternoon. It was sunny and warm with some gentle 2s and 3s and we had a lovely "t" shirt sail. Now why would I want to go out and get frozen and soaked?