Raise, he rarely has a 6, he can only chop or lose.

Disharmonist is right. All 6x hands bet turn because you are very likely to have A and not folding. So you can bluff raise allin OTR.

pot is 250+450=700; pot if split is 350 so
if you split, you pay 450 to win 350 so you have to win 450/(450+350)=56% of the time

(seems my math is correct AND faster :D)

so you if you call you hope to win a least 56% of the time, so a call is ev+ if he has a 6x less than 44% of the time; he hasn't a lot of 6x here, u have a ev+ call
but as said by LuckyMer and Disharmonist, a shove here should be better; at worst you split and at best you win 700

for fun, let's see vs which % of 6x you have an ev+ shove
pot is 250, vilain bet 450, you shove 1170
you risk 1170 to win 700, so you need to win 1170/(1170+700)=63% fold equity
if you get called by 6x you loose 1170
if you get called by Ax you split a 2600 pot so you win 1300-1170=130
if he fold you win 700

btw, we need to take in count fold equity, even if he has rarely air, because sometimes he will fold Ax
if he never fold Ax, shoving will always be worse than calling; so shoving is good only if he folds some Ax

so when we shove:
-he calls all 6x
-he calls Ax y% of the time
-he folds Ax (1-y)% of the time

let's call x the % of the time he has 6x
and y the % of the time he calls Ax

so his range is Ax + 6x, so ( y+(1-y) )*(1-x) +x = 1 ok? :)

ev shove
ev shove= -1170x + (1-x)* ( 130y + 700(1-y) )
ev shove= -1170x + (1-x) (130y + 700 -700y )
ev shove= -1170x + (1-x) ( - 570y + 700)*

ev call

when we call we win 700 if he has air, 350 if he has Ax and -450 if he has 6x
assuming he has no air (by comparing ev call and ev shove if he has air, we win 700 anyway)
ev call = 350(1-x) - 450x
ev call = 350 -350x - 450x
-> *ev call = 350 -800x

by the way, folding will be the best option when ev call = 0 so x = 350/800 = 0.44
so if you expect vilain to have more than 44% 6x, we should fold (yeah i know i already told that at the beginning, but it is worth repeating it now)

so let's compare ev call and ev shove, depending on x and y
first y stay the same and x changes
so as you can see here
and here

if he never calls Ax, shove is better if he has 6x less than 33% of the time
if he calls 10% of the time Ax, shove is better if he has 6x less than 29% of the time
if he calls 20% of the time Ax, shove is better if he has 6x less than 24% of the time
if he calls 30% of the time Ax, shove is better if he has 6x less than 20% of the time
if he calls 40% of the time Ax, shove is better if he has 6x less than 15% of the time
if he calls 45% of the time Ax, shove is better if he has 6x less than 12% of the time
if he calls 50% of the time Ax, shove is better if he has 6x less than 8% of the time
if he calls more than 55% of the time Ax, call is always better

and now we do the same here

if he never have 6x, shove is better
if he has 5% of 6x, shove is better if he calls Ax less than 55% of the time
if he has 10% of 6x, shove is better if he calls Ax less than 48% of the time
if he has 20% of 6x, shove is better if he calls Ax less than 30% of the time
if he has 30% of 6x, shove is better if he calls Ax less than 7% of the time
if he has more than 31% of 6x, call is always better
if he has more than 44% of 6x, fold is awalys better

so what did we learn?

TOO LONG DIDNT READ LOL
if he never calls Ax, shove is better if he has 6x less than 33% of the time
if he calls more than 55% of the time Ax, call is always better
if he never have 6x, shove is better if he calls Ax less than 62% of the time
if he has more than 31% of 6x, call is always better
if he has more than 44% of 6x, fold is awalys better

SOLVE
You think he has more than 44% 6x: fold
You think he has between 31% and 44% of 6x: call
You think he has some 6x (10-20%) and call all his Ax: call
You think he has less than 31% of 6x (hopefully this one): shove and look above
You think he has some 6x (10-20%) and fold more than 30% of the time his Ax: shove

so in this spot i think he has maximum 5-10% of the time 6x, so we need around 50-55% fe on his Ax to have a shove better than a call

and obviously we never fold here :)

if you want the excel file to have fun with any sizing river, any pot, any % of calling split on vilain range, and any % of he has better on vilain range on a split situation, ask me ^^