TYR Tactical has what appears to be a pretty decent deal on ESAPI plates. $293 for two level IV plates that seem pretty light for money/threat level. I see that they aren't NIJ certified and are tested to the .04 standard, but the price/weight/protection still seems attractive. I was looking at the sizes and they have small/medium that are 8.75x11.75 and large that are 10x13.

I'm about 6' tall, 175lbs and I've been using a Banshee with 10x12 swimmer cut plates, which fits great. I have another Banshee that I'd like to set up but I'm not sure which size to get. I know it's a personal preference thing to a point, but I'd greatly appreciate some direction here. I was leaning towards the small/medium, but I wasn't sure they'd be big enough... Does anyone have these plates or know anything about them? I have a little extra cash and was hoping to take advantage of some Black Friday sales to get an extra set of plates for around $300, so if you know of a better plate/deal, please let me know.

http://www.tyrtactical.com/products/details/featured-products/two-level-iv-stand-alone-esapi-plates/

Just tried a HighCom 4SAS-7 Level IV standalone measuring at 9.5" x 11.5".
The plates fits pretty loosely in the plate bag, especially on the sides but not horrible.
Also tried my BPM Level III+ standalone at 1" thick measuring at 10" x 12" and it fits very nicely.
The velcro closure on the bottom fully overlaps, so I figure a 10" x 13" will fit way better than the small/medium, which I guess will bounce around a lot more than my HigComs.
FYI I am 5'11" at 165 lbs.

I'm in the exact same boat, Small or Large for a Banshee. These plates are standard small and large SAPI sizes... having medium would be too easy for us, and likely wouldn't be at this price! Sorry I can't provide much help other than from some googling, it looks like that Large plates will fit nice and snug in the Banshee, but it won't hold XL plates.

ETA: BunkerBoots, thanks for confirming what I read!

Thanks for the input! Looks like large will fit both me and the Banshee. Before I order, are there any other level IV plates that offer this kind of performance for $300 or less?

Im 6', 190lb and wear a size large ESAPI ( mil spec sizing).  If you search there is a good plate sizing guide in this forum somewhere. Basically just make sure the top is level with your collar bone (they should sit higher than you would think), make sure it's wide enough to cover both nipples and you should be able to sit in a chair without it hitting your hips an being pushed up. These days people want to go minimalist and undersize plates to save weight but you're exposing vital organs, and might as well not wear anything if you're not going to wear the correct size of plates.