Java_Rob, if your voltage is low then you will have extended roast times regardless of bean being roasted. This is an issue with any electric roaster as the heating elements output less then what they should. You will get baked, flatter tasting coffee as you have already noted. Firstly, I would suggest you measure the voltage so we can see how much you are off; secondly, make sure you do not use an extension cord! The further you extend the less voltage is available to the roaster, so plug the roaster directly into your outlet.
As for what bean(s) to blend with the Bolivian coffee, it would really depend on what you are trying to achieve. Are you looking to make the blended result brighter, more body, etc? Thanks.