I have both the one piece grip (original Lett item) and a set of Pachmyrs on my .480 SRH. The Pachs, even though they feel thinner in my hand, soak up much more of the recoil than the one piece Letts.
The other thing about the Pachs is that they are longer than the Letts. This allows me to get a bit better grip on the gun and be able to control the recoil a little better.