I am looking forward to playing around with the TCX in by backyard to see what I can do with line to make it work better for me. It really is a great rod and despite the stiffness, it is very sensitive to even the little nibbles from small panfish.
I think that's a good idea. You won't get any less for it if you decide to sell it later than if you try to sell it now, if you keep the handle clean.
I just put a 9 wt Rio WF tropical line on my 7 wt TCX to see how it did, and was able to throw the line quite easily to 90 feet, so I seriously doubt your 6wt will feel clunky with a 7 wt on it. The TCX's have a very fast recovery rate.
You may find it easier with a WF7 to get the feel of the rod, then later switch to a WF 6 , maybe even one with a long compound taper. With that type of taper you can comfortably vary the load on the rod by increasing or decreasing the amount of line out of the tip.
With the TCR's and X's you can "tip cast" short and medium distances with light line loads and short strokes with a little practice. If that doesn't work for you, you can either stick with a 7wt on it or sell it.
I fish with both TCR's and the TCX and find them to be the nicest rods I have ever used for getting off quick casts, for things from blind casting and bass bugging, to sight fishing for flats fish.
For delicate presentations to trout on clear streams, I would still go with my little bamboo rods - though I haven't cast any of them in probably 5 years now.
I would give it a little time with the 6 wt first, and try shortening your stroke.
Then buy a cheap 7 wt WF line to play with before you decide. The shop you bought it from should certainly let you try out a demo reel with a 7 on it. Sounds like you are on speaking terms with them. MP has the shooting head weights laid out, so you can compare those weights to the AFTM specs for the first 30' of WF integrated lines.