I'll answer all your epic questions if ya want..I'm the self proclaimed Galaxy S expert..ask anyone
(who still doesn't have one FML)
The Epic 4g does have an HDMI port..it does it via the microusb port..you just need the wire which is pretty much same as an EVO...the advantages you get is you can also do video out via the 3.5mm port which while isnt HD will do a full display of the screen whats on the phone unlike the HDMI in the EVO and my guess Epic as well.
And its SUPER AMOLED not regular AMOLED..big difference >.>
Processor wise the CPU is 2x better then the EVO and graphics wise 3-4x better..of course most users may not notice it in casual use unless they play games, view videos or load web pages with flash... of course this can change with with gingerbread which is rumored to rely more on the GPU for the entire UI.
As for samsungs reputation..it isnt good in general with updates...though this time they are trying to market it as a "premium brand" so im pretty positive they will support it for at least a year..but its not like saying HTC hasn't screwed us many times either..(*cough* drivers)
Once rooted you can do free tethering either way...on both EVO and Epic
Any other questions you need answered?