This is another perennial question that is always looked at differently by different people.
Personally, since my opinion and experiences matter to
me ...
I spent too many years carrying big handguns around on and off-duty. I carried .357 Magnum & .44 Magnum revolvers IWB on my own time as a young cop, and a Colt Commander when I was willing to carry something less powerful.
Well, years of lugging big handguns around got old, and started to leave their mark. Hot spots (pressure points) eventually developed from both heavy leather gun belts (before they were called equipment belts), and toward the end of my career even lighter weight (alloy framed) compact pistols issued for my plainclothes assignment started to wear on me.
So,
for me, "comfort" is more than feeling comfortable about some gun's size & weight. It's also involved in avoiding aggravating hot spots, causing hip & knee pain, etc.
I've always thought that simple saying about "comforting versus comfortable" failed to take into consideration the wider context of carrying a weapon outside of professional requirements, too. It's one thing to belt on a gun belt for a uniform role, but another to try to conceal a weapon under soft clothes while engaged in normal, personal activities.
Capacity? For me, that's a larger risk assessment question. When I was working, at one time or another I was carrying a 6-shot revolver or a 7+1 shot pistol at one end of the "capacity" spectrum ... or a 15+1 shot pistol at the other end ... and some of my issued guns had capacities in between.
Off-duty? The same, or less.
Retirement CCW? Well, the highest capacity pistol I own only uses 12-rd mags, and the rest use 6, 7, 8, 9 & 10rd mags. I don't often carry one of my 6-shot revolvers (except when working a range session, since I enjoy shooting revolvers), but my assortment of 5-shot snubs see a lot of retirement carry use. Ditto a couple of LCP .380's I picked up, to slip in a pocket holster when my pockets are too small or too tight to conceal a 5-shot revolver.
If my travels and activities are going to take me either back to some of the "busier" jurisdictions where I used to work, or into places where local events make it seem a "working gun" is a better option, then I'll belt on one of my 6-10rd pistols (9, .40 or .45), and hope it takes a while for any lingering hot spots to become aggravated.
Spare me the "better belt & holster" thoughts, as I've acquired some great belts and holsters, and my share of not-so-great ones, and have become passingly familiar with the concepts as a LE firearms trainer.
Even the best combinations of belts and high quality holsters can still produce aggravated hot spots, after enough time. The legacy of wearing all that gear for so many years.
What's "enough" capacity? Well, might as well ask yourself how many punches (or kicks) are going to be "enough" to defend yourself in any given situation and circumstances. Dunno.
However, with a background (all of my adulthood) in various martial arts, given my druthers I'd give the emphasis and attention to a properly placed, properly executed strike, or a couple of strikes ... than a flurry of ill-timed and/or poorly performed strikes. Yes, horsepower counts, but only if delivered and utilized properly and effectively. Luck is a fickle thing.
One thing that's increasingly stood out to me when reviewing shooting incidents over the course of my career, as a firearms trainer, and especially when listening to cops who have been involved in them,
hasn't been either caliber or capacity. It's been whether or not
they were able to aim and make effective hits on their attackers.
One guy did mention he'd used "point shooting" to hit & stop his advancing, close range attacker (1 shot), but he's a rather skilled shooter, LE firearms instructor and an experienced hunter. "Gun guy". He normally emphasizes the use of "aiming", when at all possible. Practices it a lot, too.