So 40-50w brings your threshold power to at or above 6? That's quite the feat since it means you'd currently be well above 5. Are you a former pro?
There are actually many hidden motors you can get for 3000 euros and up that can provide much more than 50w. Check this one out:
http://www.vivax-assist.com/en/produkte/vivax-assist-4-0/vivax-assist_4-0.htmlGet the stealth package, hide it in the down tube, and it gives 200w for 60-90m. In running terms, that can take a normal runner size (65-70kg) 18:00 5k kind of guy (generally equal to a bit over 3w/kg) and have him easily keep up with a world class pro climber. 2800 euros, vs about 50 per thrice weekly dose of EPO. Both chump change to top pros, and its probably easier to protect your bike than your blood!