If you want the best of both worlds, look into investing into a Broncolor Mobil Power Pack and mobilite head. Broncolor has a demo Mobil system on sale right now at 50% of retail (see
www.sinarbron.com).
Mobil is a small unit that you can easily travel with and will provide far superior results as a key light over an SB800 for Portraiture. The Mobil operates on a charged battery giving you about 300 flashes per charge. And, you can use the Mobilite in combination with your SB800's (I'm a Canon shooter and I often use the Mobilite/EX550 combo for lighting when I am traveling).
On issue though. The firing of the SB800's will not sync with your Mobil if you are using the Mobil as your Master to trigger your SB800's - the SB800's will fire after a slight delay after the Mobil has fired. This is easily solved by setting your Mobil on IR/cell 'On' and using your SB800 as the triggering flash. And/or you can buy a cable to connect your SB800's directly to your Mobil unit.
You're not going to get the same quality of light with an SB800 as you will with a studio flash unit. It's all a function of how much do you want to spend, how light do you want to travel and will the differential in quality/control provided by a studio flash make a difference to your client relative to an SB800.
If your clients aren't so demanding, then you'll be able to make good portraits with a combo of SB800's and some clever use of light modifiers, bouncing light and really knowing how to control the relative output of your SB800 units to create different lighting ratios - and, you can control all of your SB800's from your Master unit - no need to run around adjusting each unit individually.
You can achieve some really creative lighting effects with a series of "on camera" flash units with the benefits of lower cost (maybe not all that much lower though) and lighter kit. I travel a lot, so I have learned how to keep my kit "lean" without sacrificing quality. I think once you start experimenting with multiple on camera flash units and how to control the output of each individual unit in your armada of flashguns, you will be amazed at how much you can simulate studio strobe lighting with on camera flashguns.
Experiment and experience! Good luck.