, 25 October 2014 (UTC)

Ok, and after this here is now the detailled technical explanation and conclusive evidence for the UE categories and their achievable throughput: The calculation of the theoretical DL throughput in MBit/s according to the largest available carrier bandwidth of 20 MHz  is as follows: A 20 MHz carrier consists of 100 Ressource Blocks (RB). Each RB consists of 12 Subcarriers (SC), which can be divided into 2 time slots (TS) each that carry 7 ODFM-Symbols each. Further we have a QAM modulation scheme. The maximum QAM specified is 64QAM, which means there are 6 bits/symbol. Additionally we have 2x2 MIMO antenna technology which allows two parallel data layers (L). In total this results in: 100 RB * 12 SC * 2 TS * 7 ODFM-Symbols * 6 bit/Symbol * 2 L = 201,6 MBit/s (Absolute theoretical technical maximum DL data rate per 20 MHz carrier). [] (page 3).
Now let's take a look at the UE categories. This information derives from the specification document 3GPP TS 36.213 [] (page 25 to 34): Let's take a look at table 7.1.7.1-1:
Cat 4 Devices use coding scheme MCS28 for DL and MCS23 for UL. This leads to TBS Index 26 for DL and 21 for UL. Looking at table 7.1.7.2.1 we now look at N_PRB (# of Ressource Blocks) = 100 (corresponds to 20 MHz carrier). For the TCS indices above we find 75376 and 51024 respectively. This results in 51,024 MBit/s for the UL. For the downlink we have 2x2 MIMO, so there are 2 Layers. Corresponding to table 7.1.7.2.2: The available number of ressource blocks 75376 (SISO) translates to 149776 for 2x2 MIMO resulting in 149,776 MBit/s ~ 150 MBit/s. As can be seen this ist a bit less than the 2*75,376=150,752 MBit/s which are stated in the 3GPP UE table Table 4.1-1 in TS 36.306.
Cat 3 Devices use coding scheme MCS23 for DL and UL. So with the explanation above we find: 51024 resulting in 51,024 MBit/s for UL again and with 2x2 MIMO for DL 101,8 MBit/s or simply 2*51,024=102,048 MBit/s (Table 4.1-1 in TS 36.306).
If we now reduce the carrier block size to 10 MHz - what happens? The amount of ressource blocks reduces from 100 to 50 - that's all. The MCS coding scheme stays the same. The conclusion is that a Cat4 device is able to achieve a theoretical troughput of 73,712 MBit/s with 10 MHz (50 RB) (Tables 7.1.7.2.1 & 7.1.7.2.2) of spectrum. Subsequently a Cat3 device in contrast can only reach 50,024 MBit/s according to these two tables and not around 75 MBit/s as previously discussed. I hope this clarified the issue so far. I doubt, that the development group is wrong here in their own specification.   20:26