I think you misrepresented the various speeds Wiltok cited. The O.P. states that his tower to device (4G) speed is 4-6 mbps. The problem is that the Ipad's network connection through the Evo's 4G only yields 1.2 mbps. Additionally, the Evo loses roughly 30% of his workplace Wi-fi bandwidth.
I'm unfamiliar with the Ipad so I don't know what, if any, anti-virus or firewalls may be on board. I know from experience that Sprint 4G Hotspot Wi-fi tether running 2.1, and AVG don't play well together. I could be getting 8+ mbps tower to device and the laptop would crap out at 1.2 mbps. In desperation for a fix, I prepared to run Trend Micro House Call and uninstalled the AVG. I went to the T.M. site to start the download and thought the laptop was a bit snappier. I ran a speed test and shazam! Problem solved... sort of. The Evo and Hotspot will eat alot of bandwidth (40%-50%). PdaNet will eat considerably less, and Easytether will eat still less yet.