I think it'd make more sense to go for the extra hp with the Mantises. For one thing, like you noted, you DO get more panel space with those. It would also let you avoid the compromises that happened to the 4-row build; whenever you condense a build, it's a good idea to try and shrink it down while still maintaining the same general functionalities, plus you can't simply put things back based on size alone; the Rene might fit, sure, but it's not intended to take up the same percentage of space if the build gets cut in half.
This is why the miniskiff issues crop up all the time. Synthesizers need FOUR specific elements: generators, modifiers, modulators, and controllers. When there's ample space, you can go with bigger modules. But if you shrink that available space down (especially this much!), you still need the same four elements AND the same proportion of those...and there IS a limit to how small this can go before you either fall into having insufficient panel space or have to make compromises that cripple a build.