First of all, all PANS-OPS procedures are designed for all engines operative (8168 - 1.1.2)
Regulatory approach climb gradient (engine out) is 2,1% (2,5% for Cat 2/3) and not 2,5% as for all engine ops, so even if you follow published missed approach procedure (2,5%) there is a risk of busting obstacle clearance
As Vilas said, missed approach is designed without acceleration segment (there is a nice picture of it in 8168)
Taking all this into account, it would be unwise to accelerate before missed app alt (or MSA if lower), unless your company has specific performance calculations or if you are not 110% sure that you will be able to accelerate and still be above required gradient during acceleration
