Echo CS 620p has a domed piston plus the 2 rings you have the higher compression.I don't think that a 590 would justifies a coil or a carb swap from a 620p.I am saying that because i don't think power difference between 2 saws is that big.Here in Greece 590 price is at 540€ (~622$) and the 620p in shindi colours (600SX) is at 660€(760$).~140$ price difference is very small,only the aluminium handlebar costs more.So if someone wants the 620 pays a little more and get it,if someone wants to save a little money gets the 590.Buy the 590 and start swapping parts just don't seems logic to me.Imho a 590 with a gasket delete,muffler mod and a retune is the perfect choise.I am waiting a 490 i bought from ebay for 230$ a couple days ago,i really like Echos but in the price of the 501SX(580$ in Greece) and the 620SX (price for it is above) i think i'll pass.Makita EA6100p is 550$,even the AT Huskies are close in price with Echos here.