Yes there is a theoretical maximum limit on the speed any sailing boat can travel at and it won't be high for any Hobie kayak, especially not for an Outback. The speed limitation is broken when the boat planes (i.e. it is no longer displacing water but skimming on top of it) but you would be hard pushed to get planing in any Hobie kayak (though it might be possible in an AI or TAI).
So yes, you are going to be limited to pretty much a "normal" paddling pace when sailing your Outback... however, there are a couple of things you can do to improve the experience:
One is to add more sail - it is not hard to add a jib and this will increase your sailing speed in light winds at the expense of increasing the risk of a capsize (i.e. makes the sailing a lot more challenging)
Another is to stay the mast - adding support to the mast to prevent the pole from bending dramatically to leeward under the press of the wind in the sail improves the shape of the sail and therefore the power that it generates. Staying the mast is almost essential for sailing with a jib (because the additional sail area causes a lot more bend in the mast to the point that both sails lose shape massively, especially upwind).
A third thing is to swap the Outback for an Adventure with daggerboard - the A is a better boat and therefore the better sailer and the daggerboard transforms the upwind sailing capabilities of the boat.
Some people add outriggers but this is not for me even though it probably means you can push the boat a bit harder when sailing.
You can also motor sail (pedal & sail) - and you can get good speeds doing this. 6-7 knots (GPS - i.e. ground "speed") is my highest consistent (over an hour or so with wind and tide in my favour) motor sailing speed to date.
Finally I would recommend resetting your expectations about sailing performance of these boats. They are not Windsurfers (I used to be a mad keen windsurfer too) Hobie 16s or performance sailboats in any conventional sense, but the challenge of sailing them well under a variety of conditions is still there and your close proximity to the water and the diminutive size of the craft makes the experience (for me) though comparatively slow, highly engaging - but it is a different sort of challenge ! The other thing I always say to people is that on these boats you rarely if ever experience a "bad" sailing day; this is because you can and would ONLY sail them when the conditions are right, which usually means warm & sunny with light winds on the beam or quarter. There is no going out in storms, no long beats to windward (unless you want to), no going out and being left wallowing on your board because the wind has dropped etc etc just perfect, challenging, uncomplicated, micro sailing, really close to the environment (which in my case is a beautiful one !). Definitely "lazy day in the park" stuff but there can be nothing like ghosting back to the beach as the sun sets over a glassy sea with a full fish bin sipping a not-quite-as-chilly-as-it-once-was one as you go. And there is an ever present risk of it all turning to custard in less than a second to keep you on your toes
As a postscript - I love tinkering & thinking through modifications/additions to improve the sailing potential of my Hobies, something which can be impossible (e.g. on a windsurfer - not much to tinker with there other than selling one sail/fin/board & buying a different one !) or very expensive (e.g. on a full-size yacht) for most sailors.. and it can be great fun and very engaging if this is the sort of thing that lights your candle. For my part I have successfully added a jib and stayed the mast, others have added round-mast roller reefing; someone has added stays and got round mast roller reefing to work (something I have tinkered with unsuccessfully); my mate (and others) has converted his Oasis into a schooner with great success; I would love to try my Adventure as a yawl (so that I can heave the boat to head-to-wind for fishing); I would love to get some kind of micro wind-vane steering working and I have bought a micro outboard with a view to putting this on my AI (it is a 2 stroke - shame on me !).
...but even in stock standard form off the shelf your Outback will probably hold its own against most other sail equipped kayaks out there.