I've been through this before with the Mellanox cards. The magic decoder ring is as follows (from Mellanox docs) ..
Adapter Card part number takes the form of "MHTS#I-XBR" where the fields are as follows
M Mellanox Technologies
H Adapter Type H = InfiniBand Host Channel Adapter, N = Ethernet Network Interface Card
T Media (Q QSFP)
S Adapter Architecture
H = ConnectX®or ConnectX-2
# # ports 1 = 1, 2 = 2
I Host Interface X = PCI-X, 4 = PCIe x4, 8 = PCIe Gen1 x8, 9 = PCIe (Gen2 x8),
G Generation <blank> = Initial product generation, B= generation B, C= generation C
- Separator
X Memory Size X = MemFree, 1=128MB, 2=256MB, 3=512MB
B Bracket S = Short, T = Tall, N = None
R RoHS <blank> = non RoHS, C = RoHS R-5 w/ Exemption, R = RoHS R-6 Lead-Free
So for the prefix "MHQH29"
field M = M to indicate a Mellanox Technologies product,
field H = H to indicate an InfiniBand Adapter Card,
field T = Q to indicate QSFP QDR,
field S = H to indicate the ConnectX family,
field # = 2 to indicate two ports,
field I = 9 to indicate PCI Express 2.0 x8 running at 5.0GT/s,
For the Suffix "XTR"
field X = X to indicate no on-board memory,
field B = T to indicate a tall bracket, and
field R = R to indicate RoHS R-6 Lead-Free
For the Suffix "XTC"
field X = X to indicate no on-board memory,
field B = T to indicate a tall bracket, and
field R = C to indicate RoHS R5 (w/ Exemptions) compliance
So both are 40Gb/s (QDR) with QSFP connectors and tall brackets, the only difference is ROHS