I'm also struggling with Hell Terror Domain with my 41 Rogue. I'm now using a Bow of the dead, which is both IAS +20% and ITD, just like the Heartseeker. I know BotD is slower than Heartseeker, gets me 1300 dps which is clearly far from enough for the level. Been farming Hell Lost Treasure for like ...

Why would you want a Heartseeker with sorc? I think you don't, but the way you stated stuff suggests that.

I think rogue is also a great first character in my opinion.

IAS means Increased Attack Speed?