DP, i'm afraid MDA's are not like a selection box, which you can't choose the one that suits.
Basically, you MUST assume an engine failure at minimums. Thats the rules to protect you and you passengers. So you have to calculate at your weight, px alt, temperature what your climb gradient is single engine from the performance section of the flight manual. you then use the appropriate minimums.
you may already know this, but in case you don't; unless otherwise stated a GA requires a minimum 2.5 degrees (actually i think it might be 2.4) climb gradient from the MDA for the required terrain separation (which varies dependant on which segment you are in). Aircraft which meet certain weight and passenger carrying capability used commecially must all be able to demonstrate the ability to meet this engine out requirement. Some airports which have restrictive minimums because of terrain are aware that some aircraft way exceed this 2.4 deg climb gradient, so they can offer less restricitve minimums requiring a higher climb gradient
however, i still do fly privately and i am aware that the same rules do not apply. as i tend not to fly when the wx is that bad, i have not had cause to refresh my knowledge on the less restrictive practices in private flying. i know for example that some multi engine aircraft can just about stay level single engine. so there is no requirement to make the 2.4 climb gradient for certification, but you could not use that aircraft bin commercial scheduled operations. we used to class the aircraft as perf A,B,C and D but the terminalology has all changed now i think.
Thats the little i know on the subject. hope it helps