Having asked the question, I feel obliged to answer it as well. I will try for extra credit.
In younger days, when we were having a lot of sex and a lot of variety, it might have been difficult to identify just one or two things that really got me off in a big way. Most often, it was probably novelty, something unexpected or a special treat. Examples would be the very rare occasions when she asked for it up her ass or, maybe, the few times she gave me an enema.
Now, in our later years, when sex is seldom and there is little variety and nothing new, my most powerful orgasms and ejaculations are the result of her masturbating me while indulging me verbally in whatever fantasy she can get into at the time. If, while this is going on, fingers on her other hand stray near, touch, or even threaten to penetrate my anus, I am immediately electrified. If, as she does only once in a blue moon, she slides a slippery, lubed finger up my ass, I am beside myself. When she does this she always stimulates my prostate to some extent, causing a strong urge, a powerful need, to ejaculate. The orgasm/ejaculation that results from having her finger up me and having my prostate stimulated while being jacked off, leaves me wiped out and takes a bit for me to recover.