Hi Bsoplinger,
Just as general awareness to those who post on this thread, as said in other posts on the topic of Tip Isolation, it all comes down to personal preference on whether one prefers foam or silicone, nothing wrong with either.
As a rule, my personal is comfort & isolation are paramount in equal measure, I don't really give about how one material over the other changes sound for as long it sounds good to me, that's all that matters as the third choice.
Personally can take both but silicone is tricker for me to find a good fit across all which is why I prefer foam but that's me.
Also aware the IT 01 has a bass vent but since there is severely minimal outside noise for me coming in, as said, I couldn't care less & this is at low volume by the way, very low volume.
So best isolation is relative, isn't it?
As long as person can enjoy whatever they're listening to without anything short of severe &/or life threatening interruption then personally all is good.
I like to point out, no matter how good or not isolation on in ears (in this case) or headphones are, if a person isn't aware of their surroundings, especially when outside as you described at any given time, then that is a serious problem, I wouldn't be blaming good isolation on that, more common sense than anything else.
By the way, just curious, why do you say silicone has better isolation for higher pitched noise or just seal in general?
With silicone & high frequencies, it all depends on the rubber's build consistency, density & thickness as not all do the same, in fact, most do jack all but I digress.
Potentially arguing about good isolation is not this thread's top & I apologise to others for this.
As a general rule, the reason why it seems to most who advocate silcone for 'blocking' or more accurately 'reducing' those high frequencies as it is generally trickier to form a good seal with foam for the same effect, all it takes is practice.
Also, most foam used as tips generally are not ear protector level as then it would be costly & not necessarily comfortable as well as sound has a way of having no vibrancy or life in certain isolation situations.
It's also why foam is generally used for ear protectors over silicone in the first place as it isn't difficult to get a good seal.
Have you actually studied, looked into or built anything where you have needed to isolate these things as in acoustic treatment to be able to enjoy full isolation?
I can tell you most people & I'm not necessarily saying professionals, will generally use foam or wool as basic isolation capable material rather than silicone as a first preference for the cost & what it can do with little effort over silicone.
Anyway, as a final note, I say overall to everyone regarding getting good isolation with in ears, use whatever works best for you & as long as it makes you happy, then you have succeeded in enjoying whatever you're listening to.
Hope everyone has a good day !
probably gonna have to pay some extra cash 
