I'm not surprised you wanted to reduce sail, especially if 20 mph ( about 17 knots) was the underlying wind and the gusts were 25 to 35 mph.
The first question to my mind is why you had a 150% headsail still up in that windspeed?
Was this windspeed not forecast by say 9am on the morning of your sail?
Willyweather has an excellent web based forecast that includes, in graphical form, windspeed, tide, temperature, and rain probability.
Generally you would change the sail before you got so out of it's range, especially if it is a reasonably reliable sea breeze or is otherwise forecast.
Also you can often reef the mainsail first depending on the sailing characteristics of your boat and how the reefing is rigged, but reefing the main is often a two or three person job unless the rigging has been adapted for singlehanded reefing.
If you are sailing in an area subject to afternoon sea breezes but start sailing in the morning and are going to stop for lunch, you might want to change down headsails at lunchtime before the seabreeze hits. Or just change down half an hour before the seabreeze is due, or as it starts to fill in, rather than waiting till it gets to 20 mph.
Unless you are racing and trying to get the last ounce of performance, life is easier if you are set up early for the expected conditions.
If you don't have multiple headsails, you might be able to get a reefing point put in your headsail so you can reduce its area by lowering it a say 3 feet (1 metre) and moving the jib cars forward to get an appropriate sheeting angle, but headsails with reefing points are not common.
Probably easier to pick up a second hand sail of appropriate size.
Normally I wouldn't want to go without a headsail completely but keep the main at full size as the main will be trying to round the boat up into the wind if there is no counterbalance from the force on a headsail.
All good points. Ummm, my Oday 30 sails very well with the full main with very strong winds. At 25 mph winds, with just the main, it sails great. Regarding the 150... that particular day I intended to use that sail under strong winds, mostly to see what the boat would do. I found out that it sails like a racing boat with those conditions (as you could imagine). I didn't lower the sail because I was worried - only because my helper didn't have enough wraps on the sheet and was getting tired of holding them since I wouldn't let him cleat them. Also a good time for lunch.
What I usually do, is put the boat as close to the wind as I can, and then, when it crosses over parallel drop the sail as quick as I can while it's over the boat. But on very strong winds, that fine line of exactly parallel (or, in Irons) is a very close point, so close in fact that it doesn't exist long enough to barely get the sail down. End result is getting beat to death by the sail while fighting it down.