It's fine to boost either one. LS's have lower compression, GSR's have better flowing heads. Dealing with VTEC and the higher compression in GSR's isn't a big deal, it's all taken care of in a competent tune. It's just said that B18B's are better than B18C's for boost because B18B's can't reach the whp levels that the B18C's can in an NA setup (with comparable mods), for one. So you might as well BOOST 'EM BABY!