My experience with wheelweights has been mixed. In low powered pistol cartridges they seem to work just fine. In some rifles, particularly if the powder charge is pretty weak, they do pretty good. In high powered rifle or pistol loads, however, accuracy for me has been, well, miserable.
My impression from reading other's posts, however, is that if you know what you are doing you can get really good performance out of wheelweights at just about any pressure level. Might have to quench them when they are made or heat them up in the oven (my wife would kill me if I tried that) but my understanding is that if you know what you are doing you can get really good performance out of wheelweights.
The 2nd edition of Lee's reloading handbook, I'm told, explains how to get good results from wheelweights.
What I find most interesting about wheelweights, however, is how emotional some people get over them. I said once that I didn't think that they performed all that well at high pressures. I learned what being flamed was all about. 54 posts on another web site call me just about every name those people could spell. Dumb, stupid, senile, etc. The e-mails I got were so profane that I had myself removed from the site. SO if you say anything bad about wheelweights you are inviting a real beating.
Also some people are VERY VERY touchy about explaining how to get good performance out of wheelweights. I don't know how to do it but I do know that asking that question can get you flamed. Why I don't know.
So my experience has been poor BUT I think if you know what you are doing wheelweights can probably be made to work well at any pressure level. Lee's 2nd handbook supposedly explains how.