QUESTION: What is the difference in case LTE is used in 800MHz band or 2600MHz band
The main difference is that at 800MHz, the RF waves are able to travel much further thus the cell size is much bigger for the same power as would be in case of 2600MHz. This means fewer eNodeB's but at the same time mean less capacity in the network. Higher frequency means smaller cell sizes and hence more cells meaning more network capacity. Other differences can be seen in the diagram above.