Holy moly. I've hit the sweet spot. I had been using trimmed biflanges for ages, but I just tried the clear silicone tips (the last ones I thought I'd end up using) and found that the trebles gain more life and the bass becomes tighter, but still with the same 'slam' when called for. No mid-bass hump at all, and wider soundstage extending out of my head compared to the relatively stereo sound of the triflanges. The wider nozzle on the tips made the trebles a tad harsh once in a while, which I solved by cutting a small ring out of the nozzle of one of the other tips, and using it like a sort of bushing – effectively increasing the nozzle length/distance between drivers and nozzle opening. This eliminated those rare bits of sibilance and made the trebles more natural. I recommend that anyone who has/had sibilance issues try this 'bushing' technique with their favourite tip, it's easy to add/remove one or two bushings and A/B in order to get the perfect sound.
A lot of people find the fiddle-factor of the W3 annoying, I find it tremendously rewarding to get the perfect sound for me by experimentation. I think it just goes to show that the variety of sounds achievable with different tips + the ability of the W3 to take to EQing very well is fantastic. IMO a product with such fine tolerances suggests the engineering required to get audio nirvana. In fact, I'd think that without this kind of fiddling it would be impossible for any IEM to reach their full potential.