Had it for a few weeks and did a few over nighters. I really love the fit and the way the pack rides, but a additional 800 or so cubic inches would be welcome. Any suggestions ?

Well, if Osprey fits, that would be a good start to stick with Osprey packs.  If you want to stick with the Stratos 36 pack, you could rig up a piggy-backed pouch or something similar.  It's not always ideal, but could add that amount of capacity you're looking for.  You just have to be careful on the weight as heavier weights carried that far out from your center of gravity may screw with your balance. I rigged up an older Maxpedition Devil Dog (lumbar style pack) to a Gregory backpack:



One area of caution is to include what your pack-weight typically is, not just volume capacity.  The Statos 36 is rated for 15-35 pounds, if you exceed that, the frame doesn't support with an effective level of comfort or performance and you'll notice on longer hikes.  Some of the higher volume packs still limit weight capacity to 35 pounds...you may prefer looking for a frame that will comfortably stabilize up to 40 pounds.  While they often say "comfort" ratings related to weight, it's more about the frame and suspension being able to handle the extra weight and not stress the frame to where you feel more weight where you shouldn't.  

An extra 800cu inches is about 13 liters, so you're likely looking for a pack with a little more volume in the 48-50 liter range, consider:

Stratos 50 liter (logical upgrade, comfort weight up to 40 pounds and similar features)
Exos 48 liter (excellent lightweight pack, weight comfort up to 40 pounds)
Atmos 50 liter (solid pack, weight comfort up to 40 pounds)
Talon 44 liter (slightly smaller, but good load-weight capacity at 40 pounds, designed for scrambling)
Kestral 48 liter (I have the older 38 liter...good volume, but not much more on weight-capacity-comfort, still only about 35 pounds)
Rook 50 (no experience, but looks pretty basic...but still tops out at 35 pounds for comfort capacity)

Again, what's your total pack weight?  I often use a ULA Circuit, but the top recommended weight is only 35 pounds.  For most 2-5 day trips, I can keep it about 30 pounds.  I recently did a trek on the AT at just over 100 miles without resupply (carried food/fuel for 9 days, finished in 7 days and a wake up) and carried about 2-3 liters of water...total starting weight was just under 40 pounds.

Summer tips, you'll likely have less weight and less bulk and compression is important.  As cooler weather hits, this is where expandable capacity comes in handy for bulky but no-so-heavy insulation or a higher rated sleeping bag.  

Just some recommendations and considerations...

ROCK6

If you can, take your sleeping bag out and strap it on the outside, top or bottom. I actually use a fairly long and narrow stuff sack and put it on one side while my thermarest is on the other side. If you're already doing that, try moving whatever tent or hammock or whatever outside too. All that stuff that has its own outer bag...