Interesting, I've used the Saunders 4550 VCCE, considered by many to be the Rolls-Royce of enlargers. It does up to 4x5 and is probably as stable as they get. I would think with the smaller units vibration would be less, not more, of a problem because there's no fan cooling or other 'moving parts'. In fact, the small footprint would, I think, allow me to dedicate an enlarger to each format (35/6x6).
I own a Beseler 67 VC. The worst, most cheaply-made, unfriendly piece of $800+ garbage I've ever bought! Nothing is geared. Everything is tension-adjusted, with the worst engineering I've ever seen in a supposedly US-made product, if this one is at all. I absolutely hate it, which is part of the reason I'm 'upgrading'.
I might just go with the Meopta Axomat 5a for 35mm, and pick up a Beseler (original - blue) 23C II for 6x6 if that would be a better combination.