When should I trade pitching for offense?

[V]

So... I have a 12 team league teams (5x5 roto), and it has a 1250 IP cap (I'm about 425 IP into the season so far) and in or near the lead in Ks/ERA/WHIP (more middle of the pack in Ws, but I'm cool with that - fluky so far this year). I also have a DEEP staff (4 SPs on the bench that cycle in when they start), and don't really sit any pitchers (no streamers).

I was thinking of getting near the 1000 IP mark before trading pitching, but am reconsidering. I'm in 2nd place (nearly 1st) and HRs is my weakest stat. Should I make deals now, and if so, who?

Team 1 Pitching staff:
SPs
CC Sabathia
Justin Verlander
Aaron Harang
Erik Bedard
Clayton Kershaw
Joba Chamberlain
Max Scherzer

RPs
Mariano Rivera
Mike Gonzalez
Scott Downs
David Aardsma

DL - John Smoltz
___________________

I have another team in a similar, but not as awesome position -

Team 2 got off to a REALLY bad offensive start (Soto+Votto+Phillips+Rollins+Aramis Ramirez was my initial infield - now have Mark Reynolds at 3B and Utley at 2B). I might target RPs, but I tend to be a bargain hunter.

SPs
Zack Greinke
CC Sabathia
Javier Vazquez
Joba Chamberlain
Cliff Lee
Max Scherzer
Rick Porcello

RPs
Mike Gonzalez
C.J. Wilson

[SDDECK]

There is no set time. You simply take a look at the league, where you stand in the league. See where you are hurting and if a trade makes sense that you feel will give you more points one way or the other you do it. A trade at any time can either make or break you.