What do you do with the tablet for clients? Show them a digital portfolio? Take notes on it?
If you're just using JPG and some app to scribble notes or type notes, you can use any tablet out there. You certainly don't need a costly tablet for this. Spend more effort on getting a portfolio gallery app that displays things the best way you want to present them. That's more important than the device they're on, other than having a nice IPS screen.
I use a 7" asus with an IPS panel and I like it for portfolio sharing. Small enough to not be crazy to carry around, bright, great battery life, and I just load it with JPG's (takes microSD which is a lot faster to load lots of quality images and other things instead of tethering, or using wifi, etc) and use the built in gallery (android) and it is great to see collages and swipe through individual images. $100.