Damn, Mr. Schwarzenegger, what kind of man-mountain are you that a 10 pound slide feels puny?
With a heavier slide, you won't be able to get it moving as fast.
The impact energy goes up by the square of the velocity, so the speed you can get the slug moving is a lot more important than the weight of the slug.
E = 1/2 m v2
where
E = dynamic energy (J, ft lb)
m = mass of the object (kg, slugs)
v = velocity of the object (m/s, ft/s)
Therefore, most people are better off with a 9 or 10 pound slug that they can get moving faster with less strain and risk of injury than with a 17 pound monster.
If your arms are somewhat longer than average and you've been eating your Wheaties, you could also get some benefit from custom building a longer slide hammer that allows you more space to get the slug moving faster.