A couple of thoughts on this subject:
1. When I brief myself for departure in a twin I use the expression "WHEN an engine fails (blah blah)" rather than "IF an engine fails (blah blah) - I think this helps with not becoming complacent. It's kind of a reminder that yes, this could very well be the most exciting departure yet!!
2. Blue line will change with weight. Have a look at the POH for the aeroplane. You may be surprised at the variation, between a full load, with full tanks, and a light fuel load and 2-3 empty seats. Blue line as marked on the ASI is for MTOW. You can work out a rule of thumb to adjust this i.e. each empty seat is worth 2 knots, empty aux tanks are worth 3 knots etc. This will not be 100% accurate to the last knot, but you will be a lot closer to flying the best speed for that particular departure, should you need to.
3. There is a Vxse as well as Vyse. Sounds obvious I know, and the difference may not be much for some aircraft. It may not even be published for others. (The 310 manual I used to refer to did have Vxse's in it). Vx is what you want for obstacle clearance, and you may be less than "blue line"but more than best angle. So you are therefore (maybe?!) in a position to proceed with the T/O - i.e. you have another option.
(P.S. Jamair I thought blue-line was Vyse?)
CR.