I'll start by saying it's easy to make my wife cum, generally. Anyone could do it. She just needs a few minutes of clit stimulation with fingers or tongue, g-spot stimulation with at least an average or so penis girth, or a few minutes of rough, fast fucking with pretty much any size (even slightly below average guys could get her off, and I've done it with like half of my penis when it was barely hard).
BUT
Girth makes a world of difference. At my natural size of about 8-8.5 inches long and 5.25-5.5 inches around, I was able to get her off with just my dick, but it took rough and deep fucking for a while. She'd lose her mind, but I would be sweating. But once we started me on an enlargement/pumping routine, holy shit. I quickly found out she enjoyed it thicker, even if it was barely noticeable to me. 5.75 inches girth made her cum a little faster and a little harder. Once I get a little above 6 inches, maybe 6.25 inches, it's almost like she cums just from getting it inside her. Her usual favorite girth is around 6.5 inches, but on the days she is willing to take more, it's AMAZING what 7 inches in girth can do! It takes a few minutes to work it in, but then instead of a deep, hard pounding, it's like I can just let it sit there and grind with the gentlest motion and she will be cumming buckets in no time. Eye rolling, body shaking orgasms with me barely making any effort. God, a true size queen is a thing of beauty.