I'll be the guinea pig.... I just ordered some of the tall ConnectX-2 brackets. Going to see if they will fit the ConnectX-3. The Mellanox store showed them in stock for $4.30 each. I studied pictures of both cards very close and as far as I can determine both the older MNPA19 single port SFP+ card and the newer MCX311A single port SFP+ cards "appear" to be virtually identical in the layout of the screw holes, bracket size, and SFP+ port hole position. They are not perforated brackets though. I'm thinking worst case they might need some minor tweaking but we will see.
I bought 8 of the MCX311A cards with the short brackets and I need tall brackets. I figure for the price I'll make them work even without the tall brackets if I have to. Once before I used a short bracket cards in tall slot system but removing the bracket and bending the top flat so it was a tiny bit taller, then used a very small drill bit and was able to drill a small hole in the narrow metal between the slots on the case to put a screw into the flattened out bracket. Worked fine too... I'd prefer to have a proper bracket though.
As far as not being perforated. I'm personally okay with that. I'll probably pull the heatsinks off, clean the garbage thermal paste off and put them back on using Arctic Silver 5. Plus on the systems I'm using them in (Dell Precision workstations) the adjacent slot blanks are all perforated so I'll still get the heat out okay. I guess you could also always get a 1/16" drill bit and perforate a solid bracket yourself if you really wanted too. lol
I'll update once I get them brackets in. Also a quick note to add.... Mellanox seems to be on the ball nowadays for shipping in stock things. Within an hour of placing my order I already have a FedEx tracking number!
If these work like I hope and if anyone needs them, I'll have a lot of 8 of the short brackets for sale for dirt cheap. I'll update on that as well once I get the full size brackets in.
Also edit to add - if it matters to anyone. This is the listing I ordered from.
Mellanox MCX311A-XCAT 10 Gigabit Ethernet PCIe Adapter Card ConnectX-3 MCX311A | eBay
The cards look great and are Rev. A5 cards. Interestingly of the 8 I got, 4 are Made in China and 4 are Made in Israel.