In reply to aln:
There's certainly lots of good Ochil country east of the Eagles/Devon road. I used to be on the committee of Friends of the Ochils, and the question of where the eastern boundary lay occasionally came up - not with any definitive conclusion, as I recall. They sort of gradually peter out in that direction, but there's definitely a case to be made that they stretch as far as Newburgh/Auchtemuchty, as the Pieman suggests. On the OS 1:50k map (Landranger 58) the S at the end of Ochil Hills sits on Ormiston Hill just south of Newburgh.
One practical boundary might be the Glen Farg road - working west from there gives lots of good options, and various of the 300m-ish hills are really nice, as are the bits of lower country between them. The area either side of the Dunning road is very good, again lots of options, and the Corb Glen pass is lovely and shouldn't be missed. Very nice grassy tops above here, with good ATV tracks leading in useful directions. Then once finally across the A823 either get on to the main spine immediately on Innerdownie and just carry on west, or go over Ben Shee (a nice shapely lump) and join the spine in the Tarmangie / Maddy Moss area.
At the western end most people would tend to treat the Sheriffmuir road as the boundary, but the 270m hill between the Waltersmuir and Cocksburn reservoirs is worth wandering over, so there's a case to be made for carrying on right down to Dunblane or Bridge of Allan for the finish.
There's a list of 300m Ochil summits here:
http://www.friendsoftheochils.org.uk/the-ochils/list-of-hills-and-maps/
All of these are west of the M90; be aware however that a couple of the ones in the area west of Glenfarg itself have crops on their gentle summits so aren't suitable for summer peakbagging - but there are lots of good ways through between them if a traverse is the main intention.