Zowie Ec1 eVo, I'd say. I have pretty big hands myself and I use a palm grip too. It uses one of the most accurate sensors on the market, has a 1000Hz polling rate, 2 thumb buttons, a really tough scrollwheel (it's not comfortable when you want to leisurely scroll down a website, but it is very precise and you will never accidentally actuate it if you have stuff bound to it), works completely driverless and I really like the shape. It's not the biggest mouse, but definitely suited for large hands. See if you could get comfortable with the shape.
Or you could get the Logitech G400s. I used the MX518 for 7+ years and I really loved the shape. The G400 was the updated version with a better sensor, and the G400s increased the DPI (which is probably uselss, but whatever) and reinforced the cable a bit. A really, really comfortable mouse, especially if you have big hands.
first thing to keep in mind. High DPI does not mean higher precision.
Zowie EC1 evo is pretty big, has an amazing sensor if you don't mind playing at 2300 dpi.
Mionix Naos 7000 might be another choice. (don't get the 8200). Its pretty big palm grip mouse. Mionix has very high reputation for build quality. Naos 7000 uses one of the two highest regarded sensors on the market and has plenty of customization for dpi to chose what you want.
If you're looking purely for size and you don't really give a shit about sensor or build quality. Mad Catz Rat gaming mice have some with lots of cutomization in size. But the only one with a decent sensor has very limited size customization, and all of them very poor reputation for build quality.
Easily the most comfortable mouse I've ever held, I currently use it on a daily basis. It's not overkill on the macro buttons, they're all placed out well, the software is easy to use, it has some nice LED controls.
It's optical, but it's also a quite large mouse. But I have small hands and even with my small hands I don't have any issues with the size. None of the macro buttons are too easy to actuate, the mouse buttons are solid, the mouse wheel is solid. It's not heavy by any means, quite light. It's definitely the most ergo mouse I've ever seen also.
Also, FUNC recently released a Rev2 of it fixing some issues with it, like a protected mouse-cable bit and they upgraded the switches for the mouse buttons for more durability and duration.