they are both great strings.....you will lose a bit of power w. the biphase..they feel a bit different..the excellerator feels more crisp and springy like nrg2 (at first), but it doesnt have the big tension loss like nrg2..i like the Excellerator..it's the next best thing to gut IMO..the biphase feels a bit more like the laserfibre supreme in that it isnt as responsive but it seems to hold tension a bit better..if you like the Excel, i would see no reason to bail for the X1 BiPhase