Honestly - if you like the SK - stick with it - it's just I noticed both yourself and Shizzle thinking about going from an SK to a guard - imho, they are on the total opposite ends of the spectrum - and if you've done 70-odd levels on one end (dps) you may be disappointed if you swap to the other end (survivability) - you have to remem too, you're both probably in starter end-game AC, non-class weapon and with only the very rare master (prob the racial/trait only) so once that changes, SK tanking (in the end game) should become a lot easier

To further explain this, I place the tanks in the following ranking for DPS (if your interested, there is a post on flames on this topic and we both happen to rank the heavy tanks in the same order):
- sk, zerk, pally, guard

Survivability is the reverse of the above

This is the reason I made the comment to Shizzle re 'you'll miss the dps if you swap to a guard'

Sks shine in dps/aoe - but let's be honest now - an average AC'd SK with an average ADP'd healer - both only being around the mid 70s in level - will find it hard to survive in karnors given that the mobs are probably white/yellow/oj? - sure, the average pair will shine with green/blue cons but above that...and karnors is a brutal wakeup given that before this time you really don't need to worry about ac, etc.