Is this too light a guage for my lotrs tremelo? ie am I better off going with .11 or .10. I bought a set of .09 and then opened it, then realised my rg is set up with .10. .09 will reduce sustain wont it?
9's should not be a problem for any kind of "floyd" trem regardless of manufacturer.
Your tone may sound slightly thinner (but only slightly), but hardly noticeable otherwise.

I don't know about the sustain issue, but there can be a number of issues that will shorten sustain. Just the mere fact that you use a tremolo means that there is less wood to vibrate, and therefore less sustain. I would hardly think that going down a size would have much effect on sustain.

Hope this helps.
perhaps .10 will be better for maintaining no fret buzz, but not sure if u can shred with .10, not that i can shred yet hahaha.