Please take the following measurements with the large pinch of salt they deserve. There are lots of caveats here:
1) I'm using a Vibro Veritas coupler, which doesn't accurately match the transfer impedance of your inner-ear. (Neither does a proper 711-compliant coupler, but at least there's some kind of standard there.) Absolute values won't match those from other measurement rigs. Deltas might not match perfectly either, but the trends should match.
2) I have mic compensation curves to account for my mic's lower sensitivity in the lows and highs.
3) I use a diffuse-field compensation correction, simply because I'm used to looking at the data that way. But it's true that all these compensation curves are somewhat arbitrary.
4) I'm using default stock white FLC eartips. The stock black FLC eartips are within measurement tolerance of the white for me. (That doesn't mean they'll be that way for you though - more pliable material might seat differently in your ear canals.) As for SpinFits - I do like them and use them a lot. They're slightly more comfortable for me, but
@Flcforrestwei has pointed out that there are differences in the treble (the wider/flared bore of the FLC tips boosts the treble around 10+ kHz). I was a skeptic about this, until I checked. Of course,
@Flcforrestwei was right
5) I'm using a StarTech sound card for the A->D and a Hugo 2 for D->A from REW.
6) Input power was the same for all cases, output normalized at 1 kHz, but note that some of the FRs have a bit of a bump around 1 kHz, which can throw off the OASPLs somewhat.
There's no right or wrong here, it just depends on personal preferences and your own ears - and recordings. My take on the above is that the modified gold (removing the damper in the gold filter) results in essentially a gold mid-range and a green-filter-like upper register.
Something interesting I figured from this... For a long time I've been wanting something between Gunmetal and Blue. You can sort of do that by taking those dampers from the gold filter and shoving them into the gunmetal (on top of the existing gunmetal filters), to create what I've called a "Double-Filtered-Gunmetal". I've put the results on a separate graph below so things don't look too cluttered:
I like this
It makes the resulting FR more like that of the KSE1500 (which, for those of you that don't know, is the current best-sounding HP on the planet - at least to my ears). This double-filtered gunmetal seems to work great in the FLC8N too, which has more energy than the FLC8S above 10 kHz. I'll need to spend more time listening to this, but this has definitely got me a whole lot more excited about the FLC8N (which I initially felt had a bit too much energy in the lower treble for my ears). At least it's another option to try on top of the 36 or 37 tuning options you already had
P.S. I don't think there's a right or wrong with the eartip choice either (i.e., SpinFit vs FLC tip). Sometimes you might want a little more treble and sometimes you might not.