Another cam question

So, I have playing with the camquest on Comp Cams website and need some clarification. Seems like on all the different cams, no matter what, the XE268 always out performs any other cam based on the dyno specs that it gives. I know that it is not exact but playing with it and adjusting the heads, valve size, carb, headers etc. etc.. the 268 always seems to out perform. If there is a difference it doesn't seem to be enough to justify having the head work done to accommodate the double valve spring set up. My specs are 340 9.5-1, rpm performer dual plane, stock 913 heads 1.88/1.60, 625 cfm edelbrock, headers, 727 with FTI 3200 stall, 323 gears and 25.3 inch tall tires. Current cam is unkown but I believe mopar purple 484.

Here is one on the xe274 and the xe268 to compare.