The lag exists for EVERY person that is using quadforce. Even crediar. I am well aware of people trying different cards. I myself have tried about 4 different cards with different clusters etc etc etc. In NO instance has the lag increased or decreased. You can experience faster loading times of levels and things of that nature.(or even not loading at all like you said) But the lag in the mkgp2 menu for instance, or the micro lag you experience every 3/4ths a second or so while racing is ALWAYS there NO MATTER WHAT. No combination of SD class or cluster size will fix that.
yes lag exists for everyone, but to varying degrees depending on class of card