I think it depends on how fast you want to go. You need big cubes or power adders to get you over 100 in a bigger single cat....plus a high dollar drive to survive for a long time.
I've got over 580ci, 660 NA hp, idles nice, easy enough to dock....but will never get into the upper 90's or 100, but i'm fine with that. I'd LOVE to have stock 6.2's, or 3.0 mercs, just as fast (or faster) and handles better. But double the filters, oil, belts, props, Oh and the initial cost lol.
But then again, changing ANYTHING on my single 28 cat may be the easiest thing ever. Need to pull a plug real quick and not get dirty or a 3rd degree burn? No-problemo!