Which one would be better for 1.5 and 2.5 sized squarebills? Or would there be no difference in performance at all?

Spool capacity and line size is your focus.

Either should work for this purpose. It comes down to preference as it pertains to profile. I don't see line capacity being critical when throwing shallow cranks.

I have the 51e and love it.  I can't see where you could go wrong with either size.

I prefer the 200E5 but that feels more comfortable in my hand and I like the slower ratio, so it's just my personal preference not really that it's better than the 50E.

I have to disagree with spool size and line capacity being your main concern. As mentioned, you are throwing shallow cranks so a 50e will hold more than enough line. If all you were throwing was the 2.5, I'd say either would be fine, but I have both reels and I throw my square bills on the 50e because I feel that it excels at throwing 1.5's and other 3/8 oz squarebills. The 200e5 will throw them too but I feel the 50e throws those smaller cranks better, and will also handle the 2.5 and other 1/2 oz cranks as well. Plus, I throw my squarebills on a 6'10" medium/moderate jerkbait blank and the size of the 50e fits my squarebill rod better IMO, and I like the 6.4:1 gear ratio for squarebills.

Both reels are the same except for size and line capacity. The 50 will throw lighter baits a little better and the 200 will throw heavier baits better. Both reels can handle everything you need it to do so keep that in mind. I have no issues throwing 1/4oz crankbaits on the 200.

 

I personally prefer the 200 size. The thumb bar is more comfortable to engage when I have to press down on it a crap load of times for fishing a moving bait. It's sort of curved downwards where as the 50 size is more horizontal and flat.

I personally use a 201E for all my squarebill fishing and have absolutely no problems or complaints. I also love my 51E but I primarily use it for plastics and jigs. No doubt in my mind though that the 51E could handle squarebill duties without complaint as well. I just "feel" more comfortable going with the 200 size for this application.

 

On a side note, that does and doesn't really pertain to the original question, I really really like the E series reels, I have 4 in the 200 size, 1 in the 50, and 1 in the 300. In my opinion Shimano really hit a home run with them. I've personally found the 200 size to be a fantastic "all purpose" workhorse reel that is super reliable and durable. Either way you choose to go you're going to be getting a very nice reel.     

I have no input but i really reall really want a 51e lol

I'd lean towards the 50 size since you probably won't be long bombing squarebills. The 200 palms well, but the 50 palms so much better, at least to me.

I have both size Curados and Cores.  My preference is the 50 simply because it fits my hand best.

 

 

 

 

It doesn't really matter.  Pay more attention to your rod choice for this.

I have not found anything the 50's can't do.  Love that size reel

i got the 2000e6 i use for squarbills the best! cant go wrong with shimano