1) Test for landscape death grip, ala Sensation (GSMArena has not published a Slide review).
2) GPS lock time and accuracy
4) Call audio quality - supposedly static and feedback heard in earpiece, and muffled at high volume. Try with speakerphone and bluetooth headset if possible.
5) HSPA+ download/upload rates.
6) Browsing experience with and without Flash content. Resize Flash content. Want to see if it's handled like the Sensation, which supposedly isn't as elegant as the Galaxy S 2.