Grade 5 to Grade 7? ABRSM to Trinity?? Help!

Hi, I've passed ABRSM grade 5 piano with merit a few months ago, and now I'm thinking of doing ABRSM grade 6 piano but as I haven't done the grade 5 theory yet I'm wondering is it possible to learn grade 5 theory alongside grade 6 piano and to pass the theory exam before I take the grade 6 piano exam? I know a bit of basic theory, but how many months would it take to learn and pass grade 5 theory if I'm spending an hour a week on it?

On a side note, how big a jump is it from ABRSM grade 5 piano to Trinity Grade 7 piano? (that way I wouldn't have to take theory and can focus on practising piano)
What are the differences between ABRSM and Trinity (above grade 6) in terms of difficulty, pieces, scales, arpeggios, sight reading, aurals, etc.

Any help would be greatly appreciated, thanks!