A slim suit in 40r will be almost the same as a 40s suit.

 That’s because a slim-fit jacket sits very close to the body with very little leg room or chest room.

But more than that, the armholes on a slim-fit suit jacket are cut much higher than a regular jacket.

So, the sleeves on a slim-fit seat will not be as long as they would be on a regular 40r jacket.

That difference in the sleeve length is the significant variation between 40r and 40s. But, that does not mean that a 40r slim fit jacket will still not be a little longer than a 40s jacket. 

But, since it holds on to the body, the difference will not be so much. However, a slim-fit jacket will look much better on a slim person and give off that defined look.

So, if that’s what you’re going for, a 40r slim fit suit will suit you better. But, a 40r slim suit will still be longer than the 40s.