I started a long time ago with an 8MOA dot in my cmore, but if you're learning, a bigger dot is MUCH better in my opinion. I've used all the way up to a 16 MOA dot in my Cmore and it is really, really fast to acquire and to use. Don't fear it being too big. It's really up to your preference. Years ago as a B shooter I got 3rd in an Area 1 standards shooting the big 16 dot !!!
I've only recently switched to a 12 MOA cmore dot and that seems to be a good balance. The bigger dots are just easier for me to track and pick up when coming in to a target. I'm probably going back to the 16 this season... I kinda miss it. The 16 rocks for steel shoots!!
For me, there aren't really any tight shots with even the 16. At 50 yards, it's the exact width of the A-zone (not that I like standards, it's just that people seem to think a big dot is a handicap on standards, and I'm tring to say it's not) Of course, I can't remember shooting much at 50 at any matches major or otherwise recently...
Lastly, head shots and other tight shots are not a problem with a big dot - the dot is considerably smaller than the target area (even the upper a zone) at the distances we usually shoot (out to 25 yards) even on partials and concealed targets.
Can you tell I like big dots? Try one - it's not that much cash, and it will really open your eyes. Just make SURE it is absolutely 100% round. If not, send it back. Football shaped dots (which I've seen lots of - go figure) don't work well regardless of their size.
Oh yeah, turn your dot down to dim on standards, if we ever have to deal with those dreaded things again, no matter what size dot you've got.