The 27 lbs heavier springs will be fine, don't worry about it.
I would suggest contacting the manufacturer of the cam you want to use and verify what weight springs they recomend for the particular cam.
Too light of a spring can result in a loss of rpms and power due to valve float while too heavy of a spring can result in premature cam and lifter wear and quite possibly breakage.
While the roller cam can free up a lot of horses due to friction loss, it isn't neccasarily required to make big power, so get what you want and at least get everything for the cam matched up so that it will last longer and take advantage of all the power that the cam has the potential for.