The web page of the hub that you are using does not specify the current of the power adapter.  This is probably your limiting factor.  You may just try the software overclocking and see if it works for you.  In most cases it is possible to replace just the power adapter with one of a higher capacity (I have done that with very cheap 10 port hubs that came with 2A power adapters which tended to die very quickly). The fan could be powered from a free USB port on your PC, or from a separate 'USB charger' adapter.

In regard to Slush reporting of hashing power, it is correct if you are hashing steadily from or before the start of a block, but as it is based on the 'shares so far' tends to be quite inaccurate if there are any changes in your hashing.  You may try another pool such as BTC for a short period of time just to check out your hashing 'on the air' if that concerns you.  Both cgminer and bfgminer provide good reporting of the hashing rates, so you can rely on that.

Cheers