This statement about 2004 being more powerful than 2005 is not true.
FS650e - 2005 has completely new engine!!!! (made specially for supermoto requirements - light and lots of torque - engine lubrication pressure circulation, trochoit oil pump, micro filter, flushable oil screen, magnetic screw, exhaust system 2-into-1, twin manifold/nickel-plated, aluminium rear muffler + titanium valves....etc...
Even with just looking at the bike, you can see enormous changes especially on engine area.
I can provide you with a few racing data, based on measurement of 2004 FS650e racing on track, and 2005 FS650e. 2004 model has 67 HP on wheel. It can outclass any bike on a twisty road - even the famous Yamaha R1 has no chance against this bike. Our testings here in Croatia, with experienced Supermoto rider and experienced Yamaha super sport rider, can confirm this. With Akrapovic exhaust you can get more horse power at higher rpm (that makes about 70-72 HP).
2005 model is more powerful than 2004. Throttle response, gear ratios, new engine construction (2004 had Enduro engine and transmision, 2005 has completely new developed engine!-supermoto spec.), and more horse power, just make 2005 supermoto a class ahead of 2004. Our test drivers here, just say that 2005 is no more "linear and elegant to drive", this bike is aggressive, sharp, powefull, its an adrenalin shot. Even Enduro riders , after trying 2005 FE450, were shocked by strength and aggressive performance of bike.
Final data - top speed 2005 FS650e (gear ratios open version 15:40) - 204 km/h.
Hope some of this helps. There should be no doubt about 2005 models. They are the best bikes has ever produced.