Tuna HP
The answer is no, smaller engines are not faster to spool up; FAR 33 has standards that apply to all engines. In any case, spool up time, in this application won't change performance numbers.
Comparing Dassault and Gulfstream is not that easy. Dassault uses lots of high-lift devices that make the slow speed arena favorable to them-their speeds are probably about 15 knots lower than GLF at equivalent weights, as is Bombardier GLEX. The advantage of the 3-engine design is exactly as you say, loss of an engine is a 33% loss of power versus 50%. Wing design is pretty much independent of number of engines. GLEX, for example, has 35 degrees of sweep, high-lift devices and the same engines as the GLF with less sweep and conventional flaps. GLF operates about 15-20 knots faster in the runway performance, but field length is pretty close for the same mission. The GLEX would be about M.05 faster in cruise, but the GLF can do that at a bit higher fuel flow.
GF