I have both the Yakima Megawarrior w/extensions and a pair of Yakima Big Powderhound SE. I the past, I would just mount the Ski/Board carrier to my megawarrior, but this winter I decided to buy the MightyMount (10V) to mount the ski/board carrier directly to the factory crossbar. 2 reasons:
1. Height clearance. I don't park my 4R in a garage at home, but I do park in parking garages at different job sites. Depending on the specific parking garage height clearance, you may have a problem. I once entered a garage with both racks on and as I headed up to the 2nd level, I heard a loud scraping noise. I slowed down and then I heard it again. As it turned out, it scraped the concrete support beams above me. I cleared the entire 1st floor without any issue and I cleared the "height caution bar" at the garage entry way, but I guess the maximum height info may be off.
Fortunately, there was no real damage to my powerhound. Surprisingly, there's barely some scratch marks. Since it was mounted to the round bars of the megawarrior, there's just enough play that it tilted slightly backwards, decreasing the overall height. So I angled the rack back a bit more and slowly drove out of that parking garage.
2. Inconvenience of mounting the Megawarrior just to install the ski/board carrier. I would just get the Mightymount to install it directly to the factory crossbars.
Don't get me wrong, the megawarrior is great for hauling stuff, but I don't use it all the time. I only mount it when I need it. There's too much wind resistence with it on, especially with a ski/board carrier tacked on.
Come to think of it, you might be able to use the load/megawarrior and a low profile ski/board carrier (FatCat) and the height may not be an issue.
BTW: Thule makes great stuff too and I'm only slightly partial to Yakima since the Megawarrior was the biggest rack I could find!