momentum
Just remember that p=m(v)
where:
p=momentum
m=mass
v=velocity
Let's forget about units and do your problem:
p1=210(1450)
p1=304,500
p2=250(1250)
p2=312,500
The 250 grain round will produce slightly more "kick", in theory.
In reality though, using the conservation of momentum law alone doesn't tell the whole story. The burn profile of the powder used can affect perceived recoil. I'm not really well versed in burn rates and what they mean, but I do believe that:
A powder that comes to to full pressure "very quickly" will all other things unchanged produced less of a perceived recoil than a slower burning powder. With the fast powder, the "duration of the kick" (I really sound like a scientist now huh lol) will be lower than with the slow powder.
Here's an example, unfortunately it's a morbid example but it's the best example I can think of. When the Challenger experienced an aerodynamic breakup in 1986, the astronauts experienced over 100 g's. On any other day 100g's would kill a man. However, since they experienced this for only a small fraction of a second, they were OK, well that is until they hit the water but we won't go there.
enjoy