Air arms s510 R in .177

[Trumpetier]

I have one of these on my radar at the moment as I'm returning to the hobby.
s410 or s510....what are the differences and should I save a few quid or spend a bit more ?

I've had many S400,s , 410,s and 510,s over the years and imo the side lever cocking of the 510 is a big improvement over the bolt on a 410

Best of the lot for me ,as I mainly hunt ,is a S510 Ultimate Sporter action dropped into a standard S400 series stock.