As some one brought up the rule book, a quick check shows that CS 25.143 defines the manoeuvre requirement for Take off all engines operating at V2 +xx as 40° before stall warning as apposed to 30° single engine at V2.
xx is the approved all engine climb speed.
So the addition 5 knots in the OP's question is to ensure the extra manoeuvre capability requirement.
as for what V2 is:
(b) V2MIN, in terms of calibrated airspeed, may not be less than –
(1) 1·13 VSR for –
(i) Two-engined and three-engined turbo-propeller powered aeroplanes; and
(ii) Turbojet powered aeroplanes without provisions for obtaining a significant reduction in the one-engine- inoperative power-on stall speed;
(2) 1·08 VSR for –
(i) Turbo-propeller
aeroplanes with more than three engines; and
(ii) Turbojet powered aeroplanes with provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed: and
(3) 1·10 times VMC established under CS 25.149.
(c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by CS 25.121(b) but may not be less than –
(1) V2MIN;
(2) VR plus the speed increment attained
(in accordance with CS 25.111(c)(2)) before reaching a height of 11 m (35 ft) above the take- off surface; and
(3) A speed that provides the manoeuvring capability specified in CS 25.143(h).