i've used sidi dominator 5s and most recently giro codes. the Codes are way more stiff than the dominators but i was never unconfortable running in the Codes. the codes have more reinforcement around the toe for abbrasions etc.
i do like the fact that the sidi has an adjustable ratchet strap while the giro code does not. so if you're feet are super narrow you may be out of luck in the giro since you'll have too much strap and not enough foot volume to cinch it down.
the giros come with toe cleats while Sidi makes you pay extra.
both pairs seems to wear well and should last you a couple of off road seasons between CX and Mtb.
Awhile back CXM did some reviews of a few different shoe models. Shoes are VERY personal, as our feet are all pretty different. You can likely get away with most mountain-oriented models, depending on the features you are looking for. Lake has a CX specific model in their line-up (Ben Berden wore it last year).
I've personally started to lean towards models with good grippy soles, as wet concrete stairs or pavement can be very slick in shoes like the Dom 5's, which have hard plastic treads that grip fine in soft stuff, but can be iceskates on hard surfaces. The unfortunate kicker is many less expensive models have those hard plastic treads and the models with a bit more rubbery grip can be pricey.
I just bought myself some Lake MX331CX shoes. Man! I can't say enough good things about em. They disappear from your feet when you're riding, they're way stiff for pedaling, and best of all for CX, have some 'killer rabbit' toe cleats for that added traction when you're toes are trying to dig in to that run-up
Pair of shoes before the Lakes were Shimano M315s. Still very stiff. Don't quite disappear from your feet like the Lakes. Cost me less too.
At least in the mid-atlantic, you're on the bike more than you're off so pedaling efficiency is a priority.