[Alonzzo2]

My setup is a RPi (openElec) with no-brand 8GB sd card, connected using edimax wireless to my NAS (nfs mount).
Everything works great, but every time I play a video (720p/1080p) it takes about 8 seconds to start. afterwards, the playback runs smoothly.
Youtube takes around 15 seconds to start to play. again, afterwards it runs smoothly.
I want to buy another Pi for the living room instead of my PC which functions also as a HTPC (will I notice a difference in the quality of the picture? maybe because of the HDMI connector?)
I want this Pi to run smoothly like in @popcornmix's video.
So I'll buy the Sandisk Cruzer Extreme 8gb and use it as the storage device and connect it using an ethernet cable,
But do I have to buy a higher quality sd card? What I get with my Pi is a no-brand 8gb.
How much impact does the storage partition (usb stick) has, and how much impact does the sd card has over the performance and the delay from when I click the 'play'?

If you install xbmc to USB, then the sdcard is only used for a couple of seconds when booting. Using the smallest (256MB or more is fine), cheapest one is fine.
Wired ethernet should make the videos start quicker than wifi.

The picture quality should be fine. If your current HTPC is connected through digital, then for HD videos it should look identical.
If you are currently using an analogue connection like VGA, then the Pi may well be better.

Great, Thanks!
From your experience, will it make a big difference if I'll buy the jetflash/sandisk ultra instead of the sandisk extreme? it's half the price