Hank,
If you measure the rider sag, then free sag, the numbers indicate the OEM springs are about right for riders of 150-160 lbs. This is subjective of course and there is room for preferences of riders. On your bike the fender extender was hitting the middle cowl - the stock fender does not do this.
That's correct about the stock fender vs fenda extenda (mine anyway), but the point of the picture isn't to show that marks were made. It's that because mine did make marks (ironically and unintentionally), it's easy to see where the forks were bottoming out.
I did measure sag before installing the sonics and it was more then 2 inches.
I don't know for sure but the picture looks like there is 3.5" of distance between the bottom of the fender and the top of the scratch marks. That leaves .75" of travel left before bottoming? Also, a rear shock damping setting set too hard allows the ST's rear end to wiggle side to side under hard braking. I have experienced this at the track and occasionally on the street when practicing emergency braking. Too soft front springs wouldn't normally have anything to do with the side to side wobble of the front wheel you describe.
All I can say is that was my experience. And the marks (ironically again) show that. They all pretty much end at the same spot. Add in how it felt when emer braking, well it's difficult to misjudge that. There was no more compression by the forks, and the hard braking pressure had no where else to go... thus the wallowing back and forth feeling of the front tire.
Not sure of significance to this, but my bike was not ABS, so of course was only doing emer braking practice on very dry roads.
Before and after I changed preload I measured front suspension travel by placing a zip tie around a fork leg and sliding it down against the dust seal. Even under tire howling emergency stops the forks still had 9 or 10 mm of travel left with the stock set up. This "poor man's data acquistion device" works quite well. I also recorded short rides over the same bumpy pavement section ending with an emergency stop with a video camera aimed at the forks. They are on my YouTube page.
When I measured sag, had some friends standing on sides to balance, me on bike with full gear. And someone in front measuring high and low after helpers on side got bike fully compressed and fully extended. Can't remember where I found this procedure, it's somewhere on the web.
Myself anyway, if I'm going to that much trouble for a spacer (which one has to do on the ST re no adjustments), I'm installing Sonic 1.2kg. They really transformed the bike to ride a lot like my 03 VFR. It wasn't harsh, just firmer, and handled bumps, corners etc much better then before.
The ST needs more preload before it needs heavier springs if a light rider is involved. That is what a rider would do if the bike had adjustable suspension - try adding preload first. Adding preload does not change spring rate or make the spring stiffer but it does increase ride height and the force necessary to start compressing the fork. But since Honda did not give us this feature, spacers can be altered to suit.
One last thing I can mention re my experience, after installing the sonics, I put a piece of masking tape over those prior marks on the inner cowling. The intention was to see how far up the new marks went compared to the old. I covered about 3/4 of the marks, all the way to the top.
Guess what? Not one new mark showed up at all. None. Zero. I was honestly shocked. In addition, there was absolutely no feeling whatsoever of bottoming out. Nothing else suspension wise had changed.
Basically, I can't recommend the sonics 1.2kg for the ST enough. On their website it's evident it's the strongest spring they make, and it only seems to be recommended for the ST, about the heaviest sport touring bike going.
The only downside to add would be that the bike didn't really change much when passing semi's in "dirty air". Still had that twitchy feeling in the front. It *may* possibly have been worse then before, did not have a chance to test it that much.