[Simon C]

I'm already Jogging after each workout for about 20 mins.
Ill give 3 sessions a week a shot, tues/thurs/sat, use sunday as a full rest day. I think I'll be ok, but if i start to feel a bit drained ill cut out one HIIT session.

I'm not sure how to rate my fitness, but I think I'm in pretty good shape. I haven't done much running at all in the last 6-12 months(used to go for 20-40min jogs), and the only thing I find now is that i get a stitch all the time, but i ignore it and keep running same pace(only done 3-4ish sessions so far).

I'll give both of those intervals a shot.

Have you followed any HIIT progressions? MR style, but harder, eg. 20/40 one week, ten 20/30, then 20/20. I'm not sure if it's needed, but after a while as fitness improves, it may be..