Dual tower coolers like the Peerless Assasin are highly recommended for gaming rigs. And as far as I know, most of these coolers if not all have the facility to adjust the front fan by manipulating the holding bracket for a couple of mm. So even if it occupies the RAM slot you can still adjust and fit the RAM unless your RAM has one of those humongous heat spreaders.
Point is, the cooler is more important than the RAM heat spreader as it makes more difference in overall performance. Those tall heat spreaders are fine with AIOs, but if you are going for a dual tower cooler, my advice will be to get one of those low profile RAM kits rather than the tall ones.