I have rather large hands as well, and I have always been comfortable with the Sanwa and Futaba radios. I find the KO to be too small. I haven't spent much time with the NB4 or the Radiomaster MT12, but have held both. They didn't feel as comfortable to me as the Sanwa and Futaba in my hand.

i have pretty big hands aswell and ive found the nb4+ to be pretty comfortable in hand out of the box

Out of the box, what other way is to have it ?

modifying it by adding grips or tennis racket wrap. changing wheels, triggers and spring tensions

there's lots of ways to do it.... i mean people 3d print stuff and swap the guts in so there are lots of other ways to have it

I don't have big hands but there's like 1/3 of the handle left when I grab my FS GT5.

I have pretty big hands as well (super wide palm and slightly above average finger length). I recently got a Spektrum iXSR and it's awesome. I installed the largest grip they have and it feels good after racing. That's how I usually test. If after a 5-7 minute race my hand and elbow (tennis elbow) don't ache or have hot-spots, it's a winner. 700 bucks be damned, it's a phenomenal radio and works well for me. Good luck, I'm sure there are cheaper options but at least with Spektrum you can probably find a local shop that has one and get a feel. I love Futaba, but they're a bit tight for me, particularly at the top of where my thumb and index finger meet. And all these new Grom, Losi Nascar and other SLT radios, ugh, I can't even use them for 60 seconds. They all get donated to the hobby store.