Dp, yes you are over thinking it just a bit, but it doesn't hurt to do so. Better than just sitting back and playing dumb.
As I had said in previous posts limb deflection might not be the same on different bows to achieve a certain draw weight. The geometry of the riser, length of the bow, and cam has an affect on which limbs are needed.
In your case you have a 2012 Bengal, right? That has the Fury XT cam and I have no info on what deflection is needed to acieve a desired draw weight. Nothing to establish a baseline to work from---until now. With your 2HP limbs and the bow being marked 45-65 I'd say that 2HP is for 60# limbs on that bow model. One thing puzzles me though. Did you read it and type it correctly? Martin bows usually have a 15# range so it should read either 45-60 or 50-65.
How about checking the brace height and a2a. Make sure they are close. If those are 603 limbs then it's possible the cables are wrapped up a bit or the string is too long. This would make the poundage high as it appears to be. It's not real critical and can be corrected very easily to drop the weight to 60#. A couple twists removed from the cables and/or adding a half dozen to the string would get it closer to 60#. OK?
So now, let's just assume that 2HP is for 60#. If you want to convert to 70# all you need to do is get 4HP limbs and you'd be all set. Or, if you leave the bow as it is (string & cable lengths) you could get 3HP limbs and should get 69.4#. Or if you're really anal about it you could get 4LP limbs and should be right at 71.4#.
Do you get it now? In other words there can be lots of options to play around with. Pertsonally I'm not real anal about draw weight. There isn't anything walking the planet that will react any differently to 64# as compared to 70#. To me draw weight is just a number and performance differences are in our heads. But the choice is yours. Whatever you decide we'll be willing to help you with it.
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