Some of this may be my opinion, but it makes sense to me, so i will voice it and say yeah man, listen to ELKA, suspension building is best done by companies like showa, ohlins, elka, works, fox, etc... i re-build them, but with thier parts, they are usually right when it comes to building shocks, they know your atv weighs 505 and they know your 150, so they should have them perfect out of the box, all you need to do is adjust them slightly to your personal preferences...
the reason i think people say add ten lbs is because people like them stiffer or that water or mud adds weight or if you have all the weight on one wheel or, i dont know, i've heard numerous reasons, but bottom line is, they can handle whatever you throw at them, i had so much mud on my rear fenders that they snapped when i jumped and guess what, my elka rear shock was still brandy new and they were only set up for your weight because i bought them used from a skinny buddy...
Suspension tuning is like a black art depending on what you believe or your riding style, you can take your shocks to 10 different shops and 10 of them will set it up different depending on thier opinion, so alp them on, try it and adjust accordingly, if its pushing, to stiff, too loose, too high, low, fast or slow, i'm pretty sure elkas tech support will be like, well turn this a quarter and try it and then turn this a half and try it and you will get em dialed in for YOUR ridin style, best of luck to you, elkas are definately on my wishlist....