6.5" insertable length is great, the average vagina is only 3.77" deep and expands to about 4.75-5.5" when aroused
The insertable length of his erect cock can be important factor for the woman's visual and physical appreciation of her man.
But my experience is that the girth of the erection is overwhelmingly more important to the woman when it comes to her being initially penetrated by it, and even more during thrusting going on to mutual orgasm.
My wife, now my ex since we amicably divorced each other for her to marry my super-spunky athletic young black buddy, gets off beautifully on well-controlled very slow opening penetration by our fully erect cocks, mine measuring 7 and 3/4 inches and his 8 and 1/2 inches in length.
But it's the girths of our erections---mine being 6 and 1/4 and his 6 and 3/4 inches measured mid-shaft---that she dotes on way more than their lengths.
The two vital parameters of length and girth of course determine the total volume of cock that during a balls-deep thrust the ideally fully stretched-up vagina comes to accommodate.
For me that volume computes to a respectable and serviceable 21 cubic inches, whilst in my young buddy's case it's a vastly more thrilling and satisfying 31 cubic inches.
The latter volume converts to 8 cubic centimeters more than than half a litre, all of it put extravagantly into the service of pumping Home between---on a good night---a mere 7 to 15 ccs of my buddy's semen, admittedly pleasuring my ex immeasurably in the process.
At orgasm the volumes of our cocks increase uncontrollably (and because they are thrust balls-deep, unmeasurably) much more for my buddy than for me, due to the sudden increase in girth the shafts and heads of our cocks undergo in the few seconds before we ejaculate, and even more during ejaculation itself.
My ex, understandably, gets off way more wildly on my buddy ejaculating in her than she ever does when I am, but even after 7 years of him and I sharing her pretty much nightly, she remains blissfully, perhaps mercifully, unaware of the gross penile volumetrics---my buddy's cock stretching her vagina an enviable 10 cubic inches (that's 50%) more than mine does---that account for her frighteningly convulsive orgasmic ecstasizings under my buddy compared to me each and every time he fucks her.
When my buddy is ejaculating in her my ex is totally transported, her face becoming a picture of open-mouthed surprise and heavenly wonder at the massiveness of his cock in her.
Shock and Awe don't even begin to describe it, especially when the orgasmic contractions and jerkings of his cock in her swell it further and finally to its supermanly maximum.
That's over-hung Black Youth for you, as I hope more than a few of you husbands of well-blacked wives know only too well.