For the T bars, anything from .92 to 1.00. Beyond 1.00 is likely a little much for actual street driving. The shocks and bars need to be matched up to get a nice result. The .92 bars would probably be happy with good parts store gas shocks. The 1.00 bars need a high end shock like Koni or Bilstein to control them. If you do not currently have a sway bar, now is the time to add one. At least the stock size bar, preferably bigger.

The XHD rear springs with their moderately higher rate would be a nice complement. Since the MP version (which I have on an E) tend to sag, may be worth trying the Eaton made springs mentioned in a previous post.