Openvswitch is like subnet manager, it turns your nic into a switch. You have to remember most CNA's have acceleration aka vswitch in silicon so think of it as a two port switch (nic). As long as your traffic stays within the nic latency would be pretty low.
Pretty much all of those 2009-2010 10gbe switches go for $1500 to 2500 these days. All built on strata broadcom.
Now if you want even cheaper : CX4 or there's the 2 or 4 port switch with 20 gigabit ports
But let's think about that. Switch with 20 ports and 2 two-port 10gbe. Hmm. Sounds a lot like what I just said up there.
The point i'm trying to say, is the whole fast networking market is a sham. It's stagnant technology and overpriced. I'll say it's price fixed..
The used price fallout makes it so obvious when 24 port switches that cost $10-20K are selling for 1/10th their price (and just as power as newer models).
The nic's are the same. New $1000-1500 CNA used $40-75.
We test all of our nic's by looping them and connecting them other car in the same box (or another near box). I've never tried Brocade since I get emulex (equal to if not better than intel) for $75. The intel dual SFP with SR optics ($129) and intel x520 10gbase-T ($150-175~) are really ancient technology.
Street price new - it's likely you would pay more for cabling (not the nic, not the switch) than "deal used ebay" server(s)!!
But i've got every fricken brand of nic here except mellanox and Brocade.
My suggestion: Always hunt for cards with optics, fiber is stupid cheap, 50meter of super high quality $61 (OM3 laser optimized), but for short haul you can use junky old OM1 or OM2 that people throw away. Many folks don't know what they are selling and will sell a nic with dual optics for $130 which is about what two optics go for. $5 of cabling and boom you are in business.
DAC cables are used in place of fiber optics for direct connection up to 5 meter. Most cards support this - not all. you may find that some nic's work quite fine out of band with dac cables. Take a close look sometime at SAS or SFP (fiber,infiniband,ethernet) and you might find the cables are pretty much the same. Obviously sas and qsfp and cx4 are different but some are really cheap to purchase and work quite fine used.
For the most part fiber is faster (light!) and uses less power than DAC cables. I think for most people using 10gbase-T will suffice. The only major benefit I see from 10gbase-T is the backwards compatibility that most cards offer to drop back to gigabit should your switch or wiring fail you can always drop down in speed.
Google pics of the inside of your favorite expensive high speed cable and you'll be surprised at what you see. I accidentally used monoprice 350mhz cat5e over 60 feet and well it ran perfectly! swapped it for cat6a and guess what, no difference in speed nor latency. $6 60 foot cable pushing 8-9 megabit over a $40 used broadcom nic from 2007 lol!