XP 650 carbs will cost a lot more than a pair of Edelbrock carbs. For your engine and your use the Edelbrocks will work fine and save you a ton of money. Or, if you're ready to go EFI get a dual Sniper setup with a Hyperspark distributor. Then you'll have full digital control of your fuel curve and ignition. You'll also have wide band feedback so you'll know what your air fuel ratio is and you'll be able to run data logs on the street or track. Something like that would answer a lot of questions that you have.