The DSD 412 will not be the weakest link, you are right the tape will. I have done similar mods using proprietary equipment. I have done slower mods (to 700fpm with iBox, and up to 500fpm with Galaxy.

Go tapeless without a doub, better yet at those speeds use a machine and gov encoder for best results. My choice would be Galaxy. That being said, it a shame to run non-p controls on a high speed job, depending on the company the proprietary controls can be much better. Again this is only my experience having worked with a bunch on equipment.